This kind of thing always makes me nervous, because you end with a mix of methods where you can (supposedly) pass arbitrary user input to them and they'll safely handle it, and methods where you can't do that without introducing vulnerabilities - but it's not at all clear which is which from the names. Ideally you design that in from the state, so any dangerous functions are very clearly dangerous from the name. But you can't easily do that down the line.
I'm also rather sceptical of things that "sanitise" HTML, both because there's a long history of them having holes, and because it's not immediately clear what that means, and what exactly is considered "safe".
You are right that the concept of "safe" is nebulous, but the goal here is specifically to be XSS-safe [1]. Elements or properties that could allow scripts to execute are removed. This functionality lives in the user agent and prevents adding unsafe elements to the DOM itself, so it should be easier to get correct than a string-to-string sanitizer. The logic of "is the element currently being added to the DOM a <script>" is fundamentally easier to get right than "does this HTML string include a script tag".
It's certainly an improvement over people trying to homebrew their own sanitisers. But that distinction of being XSS-safe is a potentially subtle one, and could end up being dangerous if people don't carefully consider whether XSS-safe is good enough when they're handling arbitrary users input like that.
Also has made me nervous for years that there's been no schema against which one can validate HTML. "You want to validate? Paste your URL into the online validation tool."
But for html snippets you can pretty much just check that tags follow a couple simple rules between <> and that they're closed or not closed correctly.
> it's not at all clear which is which from the names. Ideally you design that in from the [start]
It was, and there is: setting elementNode.textContent is safe for untrusted inputs, and setting elementNode.innerHTML is unsafe for untrusted inputs. The former will escape everything, and the latter won't escape anything.
You are right that these "sanitizers" are fundamentally confused:
> "HTML sanitization" is never going to be solved because it's not solvable.¶ There's no getting around knowing whether or any arbitrary string is legitimate markup from a trusted source or some untrusted input that needs to be treated like text. This is a hard requirement.
The Web platform folks who are responsible for getting fundamental APIs standardized and implemented natively are in a position to know better, and they should know better. This API should not have made it past proposal stage and should not have been added to browsers.
> There's no getting around knowing whether or any arbitrary string is legitimate markup from a trusted source or some untrusted input that needs to be treated like text. This is a hard requirement.
It is not a hard requirement that untrusted input is "treated like text". And this API lets you customize exactly what tags/attributes are allowed in the untrusted input. That's way better than telling everyone to write their own; it's not trivial.
> It is not a hard requirement that untrusted input is "treated like text".
Good thing that's not what I wrote, asshole. Why bother quoting me if your immediate next move is going to be to subtly alter the claim before you've even ended the very first sentence in your response?
I don't see how I differed from what you said? You divided strings going into HTML into two categories, where one category uses textContent and the other category uses innerHTML. My point is to disagree with those categories, not whatever subtle thing you're taking issue with.
I'd say I'm interested in hearing how you reason that knowing whether you need to pay at least $1000 in unpaid taxes to the IRS doesn't put you in one bucket or another, but I'm not. There is nothing worthwhile to be had in pretending that a debate with you—about this or anything else—is going to be anything other than a massive waste of time.
the browser-native Sanitizer API has one advantage the library approaches don't: it uses the same HTML parser the browser uses to render. libraries like DOMPurify parse in a separate context then re-serialize, and historically that round-trip is where most bypasses came from. when the sanitizer and the renderer share the same parser, mutation XSS attacks have nowhere to hide.
BTW, HTML allows inline SVG with an XML-flavored syntax that interprets <script/> and <title> differently. It's a goldmine for sanitizer escapes. There are completely bonkers syntax switching and error recovery rules that interact with parsing modes (there's even an edge case where a particular attribute value switches between HTML and XML-ish parsing rules).
Don't even try to allow inline <svg> from untrusted sources! (and then you still must sanitise any svg files you host)
It may be using some of the same deserialization machinery, but "parsing" is a broad term that includes things that the sanitizer is doing and that the browser's ordinary content-processing → rendering path does not.
Even with this being a native API, there are still two parsers that need to be maintained. What a native API achieves is to shift the onus for maintaining synchronicity between the two onto the browser makers. That's not nothing, but it's also not the sort of free lunch that some people naively believe it is.
Ideally you should be able to set a global property somewhere (as a web developer) that disallows outdated APIs like `innerHTML`, but with the Big Caveat that your website will not work on browsers older than X. But maybe there's web standards for that already, backup content if a browser is considered outdated.
It's not an "outdated API". It's still good for what it was always meant for: parsing trusted, application-generated markup and atomically inserting it into the content tree as a replacement for a given element's existing children.
> set a global property somewhere (as a web developer) that disallows[…] `innerHTML`
The idea is you wouldn't mix innerHTML and setHTML, you would eliminate all usage of innerHTML and use the new setHTMLUnsafe if you needed the old functionality.
Right. Like how any potential reader is familiar with the risks of sql injection which is why nothing has ever been hacked that way.
Or how any potential driver is familiar with seat belts which is why everybody wears them and nobody’s been thrown from a car since they were invented.
So we shouldn’t mark anything as unsafe then? And give no indication whatsoever?
The issue isn’t that the word “safe” doesn’t appear in safe variants, it’s that “unsafe” makes your intentions clear: “I know this is unsafe, but it’s fine because of X and Y”.
If you want to adopt this in your project, you can add a linter that explicitly bans innerHTML (and then go fix the issues it finds). Obviously Mozilla cannot magically fix the code of every website on the web but the tools exist for _your_ website.
I kinda like the way JS evolved into a modern language, where essentially ~everyone uses a linter that e.g. prevents the use of `var`. Sure, it's technically still in the language, but it's almost never used anymore.
(Assuming transpilers have stopped outputting it, which I'm not confident about.)
Depending on the transpiler and mode of operation, `var` is sometimes emitted.
For example, esbuild will emit var when targeting ESM, for performance and minification reasons. Because ESM has its own inherent scope barrier, this is fine, but it won't apply the same optimizations when targeting (e.g.) IIFE, because it's not fine in that context.
Yeah, using a kilowatt GPU for string replacement is going to be the killer feature. I probably shouldn't even be joking, people are using it like this already
This one is literally matching "innerHTML = X" and setting "setHTML(X)" instead. Not some complex data format transformation
But I can see what you mean, even if then it would still be better for it to print the code that does what you want (uses a few Wh) than doing the actual transformation itself (prone to mistakes, injection attacks, and uses however many tokens your input data is)
My experience is that they somehow print quite modern code despite things like ES6 being too new to be standard knowledge even for me and I'm not even middle-aged yet
Maybe the last 10 years saw so much more modern code than the last cumulative 40+ years of coding and so modern code is statistically more likely to be output? Or maybe they assign higher weights to more recent commits/sources during training? Not sure but it seems to be good at picking this up. And you can always feed the info into its context window until then
This is not my experience. Claude has been happily generating code over the past week that is full of implicit any and using code that's been deprecated for at least 2 years.
>> Maybe the last 10 years saw so much more modern code than the last cumulative 40+ years of coding and so modern code is statistically more likely to be output?
The rate of change has made defining "modern" even more difficult and the timeframe brief, plus all that new code is based on old code, so it's more like a leaning tower than some sort of solid foundation.
Theoretically, if you could train your own, and remove all references to the deprecated code in the training data, it wouldn't be able to emit deprecated code. Realistically that ability is out of reach at the hobbiest level so it will have to remain theoretical for at least a few more iterations of Moore's law.
Edit: I don't mean this flippantly. If I want to render, say, my blog entry on your site, will I need to select every markup element from a dropdown list of custom elements that only accept text a la Wordpress?
That's why I only allow user input of alphanumeric ascii characters. No need to worry about sanitation then, and you can just remove all the characters that don't match.
(It's a joke, but it is also 100% XSS, SQL injection, etc. safe and future proof)
> I'm also rather sceptical of things that "sanitise" HTML, both because there's a long history of them having holes, and because it's not immediately clear what that means, and what exactly is considered "safe".
What is safe depends on where the sanitized HTML is going, on what you're doing with it.
It isn't possible to "sanitize HTML" after collecting it so that, when you use it in the future, it will be safe. "Safe" is defined by the use.
But it is possible to sanitize it before using it, when you know what the use will be.
If that'd been the design from the start, then sure. But it's not at all obvious that setHTML is safe with arbitrary user input (for a given value of "safe") and innerHTML is dangerous.
At this point that API has been around for decades and is probably impossible to deprecate without breaking fairly large amounts of the web. The only option is to introduce a new and better API, and maybe eventually have the browser throw out console warnings if a page still uses the old innerHTML API. I doubt any browser vendor will be gung ho enough to actually remove it for a very long time.
Great to see this start to show up, but it looks like it will be a while before browser support is widely distributed enough to rely on it being present: https://caniuse.com/mdn-api_element_sethtml
I wouldn't advise polyfills on this one, it entirely depends on the browser ability to evaluate cross scripting and cross origin rule on a arbitrary snippet. This is not a convenience API.
So you can still inject <h1> or <br><br><br>...
etc into your username, in the given example
Preventing one bug class (script execution) is good, but this still allows arbitrary markup to the page (even <style> CSS rules) if I'm reading the docs correctly. You could give Paypal a fresh look for anyone who opens your profile page, if they use this. Who would ever want this?
The main case I can think of is wanting some forum functionality. Perhaps you want to allow your users to be able to write in markdown. This would provide an extra layer of protection as you could take the HTML generated from the markdown and further lock it down to only an allowed set of elements like `h1`. Just in case someone tried some of the markdown escape hatches that you didn't expect.
I think this might be the answer. There's no point to it by itself (either you separate data and code or you don't and let the user do anything to your page), but if you're already using a sanitiser and you can't use `textContent` because (such as with Markdown) there'll be HTML tags in the output, then this could be extra hardening. Thanks!
`setHTML` is meant as a replacement for `innerHTML`. In the use case you describe, you would have never wanted `innerHTML` anyway. You'd want `innerText` or `textContent`.
> If the default configuration of setHTML( ) is too strict (or not strict enough) for a given use case, developers can provide a custom configuration that defines which HTML elements and attributes should be kept or removed.
Injecting markup into someone else's website isn't what I'd call too strict a default configuration
If you mean to convey that it's possible to configure it to filter properly, let me introduce you to `textContent` which is older than Firefox (I'm struggling to find a date it's so old)
It sounds like you're arguing against a specific usecase, rather than the technology itself. If you don't want arbitrary markup in usernames, setHTML would absolutely be the wrong choice, but that's not really a good argument against setHTML.
Or I guess you could completely restyle and change the text of UI elements so it looks like the user is doing one thing when they're actually doing something completely different like sending you money
Back in 2002 (?) I got banned from a certain auction site because I managed to inject HTML into my username that made it so once I had bid the "Bid" button disappeared for all subsequent users.
will strip all elements out. That's not too difficult.
Plus this is defense-in-depth. Backends will still need to sanitize usernames on some standard anyhow (there's not a lot of systems out there that should take arbitrary Unicode input as usernames), and backends SHOULD (in the RFC sense [1]) still HTML-escape anything they output that they don't want to be raw HTML.
i think the use case for setHTML is for user content that contains rich text and to display that safely. so this is not an alternative for escaping text or inserting text into the DOM but rather a method for displaying rich text. for example maybe you have an editor that produces em, and strong tags so now you can just whitelist those tags and use setHTML to safely put that rich text into the DOM without worrying about all the possible HTML parsing edge cases.
> How exactly, given that setHTML sanitizes the input?
The article says that the output is:
<h1>Hello my name is</h1>
So it keeps (non-script) html tags (and presumably also attributes) in the input. Idk how you're asking "how" since it's the default behavior
Stripping HTML tags completely has always been possible with the drop-in replacement `textContent`. Making a custom configuration object for that is much more roundabout
Yes, because that's the default configuration, if you don't want that, stop using the default configuration? It's still sanitizing away the common XSS holes, hence it's a safer alternative to .innerHTML, and a more flexible alternative to .innerText
Shouldn't use innerText anyway (nonstandard, worse performance, tries to parse the HTML and gives you unexpected behavior if e.g. a style is set that makes an element invisible but still has text inside, doesn't work on all DOM nodes...)
I can see how it's a way of allowing some tags like bold and italic without needing a library or some custom parser, but I didn't understand what the point of this default could be and so why it exists (a sibling comment proposed a plausible answer: hardening on top of another solution)
> Yes, because that's the default configuration, if you don't want that, stop using the default configuration?
"don't use it if it's not what you want" is perhaps the silliest possible answer to the question "what's the use-case for this"
> Shouldn't use innerText anyway (nonstandard, worse performance, tries to parse the HTML and gives you unexpected behavior if e.g. a style is set that makes an element invisible but still has text inside, doesn't work on all DOM nodes...)
Maybe you meant .innerHTML? .innerText AFAIK doesn't try to parse HTML (why would it?), but I don't understand what you mean with nonstandard, both .innerHTML and .innerText are part of the standards, and I think they've been for a long time.
> but I didn't understand what the point of this default could be and so why it exists (a sibling comment proposed a plausible answer: hardening on top of another solution) [...] the question "what's the use-case for this"
I guess maybe third time could be the charm: it's for preventing XSS holes that are very common when people use .innerHTML
> maybe third time could be the charm: it's for preventing XSS holes
That information is in the question, so sadly no this still doesn't make sense to me because I don't understand any scenario in which this is what the developer wants. You always still need more code (to filter the right tags) or can just use textContent (separating data and code completely, imo the recommended solution)
> Maybe you meant .innerHTML? .innerText AFAIK doesn't try to parse HTML (why would it?)
No, I didn't mean that, yes it does, and no I don't know why it is this way. If you don't believe me and don't want to check it out for yourself, I'm not sure what more I can say
It seems like the goal of the default configuration is preventing script injection while being otherwise very permissive. Basically, "safer than innerHTML, even when used very lazily". But I would expect guidance to evolve saying that it almost never makes sense to use the default and instead to specify a configuration that makes contextual sense for a given field.
The default might be suitable for something like an internal blog where you want to allow people to sometimes go crazy with `<style>` tags etc, just not inject scripts, but I would expect it to almost always make sense to define a specific allowed tag and attribute list, as is usually done with the userland predecessors to this API.
Anyone who wants to provide some level of flexibility but within bounds. Say, you want to allow <strong> and <em> in a forum post but not <script>. It's not too difficult to imagine uses.
And is that sanitization perfect? Kept up to date?
With a safe API like this one that's tied to the browser's own interpretation of HTML (i.e. it is perfectly placed to know exactly what is and isn't dangerous given it is the one rendering it) wouldn't it be much better to rely on that?
What I really want is a <sandbox> element that can safely run dangerous code, not something that modifies dangerous code.
Iframes have significant restrictions as they can’t flow with the DOM. With AI and the increase in dynamic content, there’s going to be even more situations where you run untrusted code. I want configurable encapsulation.
Title was a bit rage-baity. And I think you can already do sanitation by writing a function to check input before passing it to innerHTML?
This really just seems like another attempt at reinventing the wheel. Somewhat related, I find it ironic how i cannot browse hacks.mozilla.org in my old version of firefox("Browser not supported"). Also, developer.mozilla.org loads mangled to various degrees in current versions of palemoon, basilisk, and seamonkey
It's like there is some sort of "browser cartel" trying to screw up The Web.
Seems like this has a bunch of footguns. Particularly if you interact with the Sanitizer api, and particularly if you use the "remove" sanitizer api.
Don't get me wrong, better than nothing, but also really really consider just using "setText" instead and never allow the user to add any sort of HTML too the document.
Using an allowlist based Sanitizer you are definitely less likely to shoot yourself in the foot, but as long as you use setHTML you can't introduce XSS at least.
This is nice. The best part is that all aspects of network access are now properly controlled so that security transitioned from a chain of trusted code to a chain of trusted security setup on hosts, with existing workable safe defaults.
naming the old behavior setHTMLUnsafe is what did it for me. security features that require developers to opt in don't work. making the unsafe path feel unsafe does.
It is a fairly small thing, but ... really. One day someone should clean up the mess that is JavaScript. Guess it will never happen, but JavaScript has so many strange things ...
I understand that this here is about protection against attacks rather than a better API design, but really - APIs should ideally be as great as possible the moment they are introduced and shown to the public.
I don’t really think it’s pedantic it’s just that unless you preface a lot of comments on HN these days, you’ll get a lot of whataboutism and straw man arguments.
is there any situation where innerHTML would be preferable? I could suppose it might be more performant and so if you were constructing something that was not open to XSS it might theoretically be better (with the usual caveat that people always make mistakes about this kind of thing)
When browsers implement a variant that lets you separate data and code perhaps. That's what I expected when reading the headline: setHtml(code, data, data, ...), just like parameterised SQL works: prepare("select rowid from %s where time < %n", tablename, mynumber)
This new method they've cooked up would be called eval(code,options) if html was anything other than a markup language
It would close the loop better if you could also use policy to switch off innerHTML in a given page, but definitely a step in the right direction for plain-JavaScript applications.
This kind of thing always makes me nervous, because you end with a mix of methods where you can (supposedly) pass arbitrary user input to them and they'll safely handle it, and methods where you can't do that without introducing vulnerabilities - but it's not at all clear which is which from the names. Ideally you design that in from the state, so any dangerous functions are very clearly dangerous from the name. But you can't easily do that down the line.
I'm also rather sceptical of things that "sanitise" HTML, both because there's a long history of them having holes, and because it's not immediately clear what that means, and what exactly is considered "safe".
You are right that the concept of "safe" is nebulous, but the goal here is specifically to be XSS-safe [1]. Elements or properties that could allow scripts to execute are removed. This functionality lives in the user agent and prevents adding unsafe elements to the DOM itself, so it should be easier to get correct than a string-to-string sanitizer. The logic of "is the element currently being added to the DOM a <script>" is fundamentally easier to get right than "does this HTML string include a script tag".
[1] https://developer.mozilla.org/en-US/docs/Web/API/Element/set...
It's certainly an improvement over people trying to homebrew their own sanitisers. But that distinction of being XSS-safe is a potentially subtle one, and could end up being dangerous if people don't carefully consider whether XSS-safe is good enough when they're handling arbitrary users input like that.
Also has made me nervous for years that there's been no schema against which one can validate HTML. "You want to validate? Paste your URL into the online validation tool."
This help? https://github.com/validator/validator
But for html snippets you can pretty much just check that tags follow a couple simple rules between <> and that they're closed or not closed correctly.
That app does look helpful!
> it's not at all clear which is which from the names. Ideally you design that in from the [start]
It was, and there is: setting elementNode.textContent is safe for untrusted inputs, and setting elementNode.innerHTML is unsafe for untrusted inputs. The former will escape everything, and the latter won't escape anything.
You are right that these "sanitizers" are fundamentally confused:
> "HTML sanitization" is never going to be solved because it's not solvable.¶ There's no getting around knowing whether or any arbitrary string is legitimate markup from a trusted source or some untrusted input that needs to be treated like text. This is a hard requirement.
<https://news.ycombinator.com/item?id=46222923>
The Web platform folks who are responsible for getting fundamental APIs standardized and implemented natively are in a position to know better, and they should know better. This API should not have made it past proposal stage and should not have been added to browsers.
> There's no getting around knowing whether or any arbitrary string is legitimate markup from a trusted source or some untrusted input that needs to be treated like text. This is a hard requirement.
It is not a hard requirement that untrusted input is "treated like text". And this API lets you customize exactly what tags/attributes are allowed in the untrusted input. That's way better than telling everyone to write their own; it's not trivial.
Your shitty strawman is shitty.
> It is not a hard requirement that untrusted input is "treated like text".
Good thing that's not what I wrote, asshole. Why bother quoting me if your immediate next move is going to be to subtly alter the claim before you've even ended the very first sentence in your response?
Go fuck yourself.
I don't see how I differed from what you said? You divided strings going into HTML into two categories, where one category uses textContent and the other category uses innerHTML. My point is to disagree with those categories, not whatever subtle thing you're taking issue with.
Oh, okay. Tell me, dipshit, are the follow two claims equivalent or different?:
"Everyone who files a tax return should know whether they need to pay at least $1000 in unpaid taxes to the IRS."
"Everyone who files a tax return needs to pay at least $1000 in unpaid taxes to the IRS."
This is a totally different kind of statement. You're not dividing tax returns into two categories and then saying what to do with each category.
Those claims are different but not in a way that analogizes to the HTML conversation.
I'd say I'm interested in hearing how you reason that knowing whether you need to pay at least $1000 in unpaid taxes to the IRS doesn't put you in one bucket or another, but I'm not. There is nothing worthwhile to be had in pretending that a debate with you—about this or anything else—is going to be anything other than a massive waste of time.
the browser-native Sanitizer API has one advantage the library approaches don't: it uses the same HTML parser the browser uses to render. libraries like DOMPurify parse in a separate context then re-serialize, and historically that round-trip is where most bypasses came from. when the sanitizer and the renderer share the same parser, mutation XSS attacks have nowhere to hide.
BTW, HTML allows inline SVG with an XML-flavored syntax that interprets <script/> and <title> differently. It's a goldmine for sanitizer escapes. There are completely bonkers syntax switching and error recovery rules that interact with parsing modes (there's even an edge case where a particular attribute value switches between HTML and XML-ish parsing rules).
Don't even try to allow inline <svg> from untrusted sources! (and then you still must sanitise any svg files you host)
If you just serve SVGs through <img> tag it’ll be much safer. I never understood the appeal of inline <svg> anyways.
Inline SVG is stylable with CSS styles in the same HTML page.
Also animatible with the same context (Animation API, etc.) as the parent page, so different SVGs can influence each other’s animations.
Inline reduces round trips.
You can use img with a data url?
It may be using some of the same deserialization machinery, but "parsing" is a broad term that includes things that the sanitizer is doing and that the browser's ordinary content-processing → rendering path does not.
Even with this being a native API, there are still two parsers that need to be maintained. What a native API achieves is to shift the onus for maintaining synchronicity between the two onto the browser makers. That's not nothing, but it's also not the sort of free lunch that some people naively believe it is.
Ideally you should be able to set a global property somewhere (as a web developer) that disallows outdated APIs like `innerHTML`, but with the Big Caveat that your website will not work on browsers older than X. But maybe there's web standards for that already, backup content if a browser is considered outdated.
It's not an "outdated API". It's still good for what it was always meant for: parsing trusted, application-generated markup and atomically inserting it into the content tree as a replacement for a given element's existing children.
> set a global property somewhere (as a web developer) that disallows[…] `innerHTML`
(Not that you should actually do this—anyone who has to resort to it in their codebase has deeper problems.)Doesn't using TrustedTypes basically do that? I'm not really web-y, someone please correct me if I'm off.
Yup, this is basically what TrustedTypes is for!
I like the idea of that. But I imagine linting rules are a much more immediate answer in a lot of projects.
The idea is you wouldn't mix innerHTML and setHTML, you would eliminate all usage of innerHTML and use the new setHTMLUnsafe if you needed the old functionality.
I looked up setHTMLUnsafe on MDN, and it looks like its been in every notable browser since last year.
Good idea to ship that one first, when it's easier to implement and is going to be the unsafe fallback going forward.
I looked up setHTMLUnsafe on MDN, and it looks like its been in every notable browser since last year.
Oddly though, the Sanitizer API that it's built on doesn't appear to be in Safari. https://developer.mozilla.org/en-US/docs/Web/API/Sanitizer
If I need the old functionality why not stick to innerHTML?
because the "unsafe" suffix conveys information to the reader, whereas `innherHTML` does not?
Any potential reader should be familiar with innerHTML.
Right. Like how any potential reader is familiar with the risks of sql injection which is why nothing has ever been hacked that way.
Or how any potential driver is familiar with seat belts which is why everybody wears them and nobody’s been thrown from a car since they were invented.
yes, and bugs shouldn't exist because everyone should be familiar with everything.
But if some are marked unsafe and others are not it gives a false sense of security if something is not marked unsafe.
So we shouldn’t mark anything as unsafe then? And give no indication whatsoever?
The issue isn’t that the word “safe” doesn’t appear in safe variants, it’s that “unsafe” makes your intentions clear: “I know this is unsafe, but it’s fine because of X and Y”.
Maybe we should add the word safe and consider everything else as unsafe
Like life, things should default to being safe. Unsafe, unexpected behaviours should be exception and thus require an exceptional name.
Legacy and backwards compatibility hampers this, but going forward…
Because then your linter won't be able to tell you when you're done migrating the calls that can be migrated.
Because sooner or later it'll be removed.
No because the web has to remain backwards compatible with older sites. This has always been the case.
And break millions of sites?
You can't rename an existing method. It would break compatibility with existing websites.
> you would eliminate all usage of innerHTML
The mythical refactor where all deprecated code is replaced with modern code. I'm not sure it has ever happened.
I don't have an alternative of course, adding new methods while keeping the old ones is the only way to edit an append-only standard like the web.
If you want to adopt this in your project, you can add a linter that explicitly bans innerHTML (and then go fix the issues it finds). Obviously Mozilla cannot magically fix the code of every website on the web but the tools exist for _your_ website.
I kinda like the way JS evolved into a modern language, where essentially ~everyone uses a linter that e.g. prevents the use of `var`. Sure, it's technically still in the language, but it's almost never used anymore.
(Assuming transpilers have stopped outputting it, which I'm not confident about.)
I touch JS that uses var heavily on a daily basis and I would be incredibly surprised to find out that I am alone in that.
Actually... https://github.com/microsoft/TypeScript/issues/52924
Ah yeah, I remember that. General point still stands: in terms of the lived experience of developers, `var` is essentially deprecated.
for some values of "everyone" and "never".
Depending on the transpiler and mode of operation, `var` is sometimes emitted.
For example, esbuild will emit var when targeting ESM, for performance and minification reasons. Because ESM has its own inherent scope barrier, this is fine, but it won't apply the same optimizations when targeting (e.g.) IIFE, because it's not fine in that context.
https://github.com/evanw/esbuild/issues/1301
It for sure happens for drop in replacements.
Nobody's talking about old code here.
Having an alternative to innerHTML means you can ban it from new code through linting.
Finally, a good use case for AI.
Yeah, using a kilowatt GPU for string replacement is going to be the killer feature. I probably shouldn't even be joking, people are using it like this already
When the condition for when you want to replace is hard to properly specify, AI shines for such find and replaces.
This one is literally matching "innerHTML = X" and setting "setHTML(X)" instead. Not some complex data format transformation
But I can see what you mean, even if then it would still be better for it to print the code that does what you want (uses a few Wh) than doing the actual transformation itself (prone to mistakes, injection attacks, and uses however many tokens your input data is)
That can break the site if you do the find and replace blindly. The goal here is to do the refactor without breaking the site.
> When the condition for when you want to replace is hard to properly specify, AI shines for such find and replaces.
And, in your opinion, this is one of those cases?
This ship has sailed unfortunately, no later than yesterday I've seen coworkers redact a screenshot using chatGTP.
Wouldn't AI be trained on data using innerHTML?
My experience is that they somehow print quite modern code despite things like ES6 being too new to be standard knowledge even for me and I'm not even middle-aged yet
Maybe the last 10 years saw so much more modern code than the last cumulative 40+ years of coding and so modern code is statistically more likely to be output? Or maybe they assign higher weights to more recent commits/sources during training? Not sure but it seems to be good at picking this up. And you can always feed the info into its context window until then
This is not my experience. Claude has been happily generating code over the past week that is full of implicit any and using code that's been deprecated for at least 2 years.
>> Maybe the last 10 years saw so much more modern code than the last cumulative 40+ years of coding and so modern code is statistically more likely to be output?
The rate of change has made defining "modern" even more difficult and the timeframe brief, plus all that new code is based on old code, so it's more like a leaning tower than some sort of solid foundation.
ES6 is 11 years old. It's not that new.
> "ES6 being too new to be standard knowledge"
Huh? It's been a decade.
Which is why it can easily understand how innerHTML is being used so that it can replace it with the right thing.
Honest question: Is there a way to get an LLM to stop emitting deprecated code?
Theoretically, if you could train your own, and remove all references to the deprecated code in the training data, it wouldn't be able to emit deprecated code. Realistically that ability is out of reach at the hobbiest level so it will have to remain theoretical for at least a few more iterations of Moore's law.
fwiw, if you serve your page with:
Content-Security-Policy: require-trusted-types-for 'script'
…then it blocks you from passing regular strings to the methods that don't sanitize.
They do link the default configuration for "safe": https://wicg.github.io/sanitizer-api/#built-in-safe-default-...
But I agree, my default approach has usually been to only use innerText if it has untrusted content:
So if their demo is this:
Mine would be:What if I wanted an <h2>?
Edit: I don't mean this flippantly. If I want to render, say, my blog entry on your site, will I need to select every markup element from a dropdown list of custom elements that only accept text a la Wordpress?
That's why I only allow user input of alphanumeric ascii characters. No need to worry about sanitation then, and you can just remove all the characters that don't match.
(It's a joke, but it is also 100% XSS, SQL injection, etc. safe and future proof)
> I'm also rather sceptical of things that "sanitise" HTML, both because there's a long history of them having holes, and because it's not immediately clear what that means, and what exactly is considered "safe".
What is safe depends on where the sanitized HTML is going, on what you're doing with it.
It isn't possible to "sanitize HTML" after collecting it so that, when you use it in the future, it will be safe. "Safe" is defined by the use.
But it is possible to sanitize it before using it, when you know what the use will be.
Some sanitization is better than none? If you're relying on the browser to handle it for you, you're already in a lot of trouble.
realSetSafeHTML()
it's not at all clear which is which from the names
There's setHTML and setHTMLUnsafe. That seems about as clear as you can get.
If that'd been the design from the start, then sure. But it's not at all obvious that setHTML is safe with arbitrary user input (for a given value of "safe") and innerHTML is dangerous.
But you can use InnerHTML to set HTML and that's not safe.
At this point that API has been around for decades and is probably impossible to deprecate without breaking fairly large amounts of the web. The only option is to introduce a new and better API, and maybe eventually have the browser throw out console warnings if a page still uses the old innerHTML API. I doubt any browser vendor will be gung ho enough to actually remove it for a very long time.
Great to see this start to show up, but it looks like it will be a while before browser support is widely distributed enough to rely on it being present: https://caniuse.com/mdn-api_element_sethtml
Indeed, as any browser API, it might be for in a few years (months if happy with the most recent versions), and we may have polyfills in the meantime.
I wouldn't advise polyfills on this one, it entirely depends on the browser ability to evaluate cross scripting and cross origin rule on a arbitrary snippet. This is not a convenience API.
So you can still inject <h1> or <br><br><br>... etc into your username, in the given example
Preventing one bug class (script execution) is good, but this still allows arbitrary markup to the page (even <style> CSS rules) if I'm reading the docs correctly. You could give Paypal a fresh look for anyone who opens your profile page, if they use this. Who would ever want this?
> Who would ever want this?
The main case I can think of is wanting some forum functionality. Perhaps you want to allow your users to be able to write in markdown. This would provide an extra layer of protection as you could take the HTML generated from the markdown and further lock it down to only an allowed set of elements like `h1`. Just in case someone tried some of the markdown escape hatches that you didn't expect.
> This would provide an extra layer of protection
I think this might be the answer. There's no point to it by itself (either you separate data and code or you don't and let the user do anything to your page), but if you're already using a sanitiser and you can't use `textContent` because (such as with Markdown) there'll be HTML tags in the output, then this could be extra hardening. Thanks!
You'd never want to store the processed HTML anyway, this is website building 101.
I store both, to serve processed HTML faster, and to be able to rebuild it just in case. Is this ok?
`setHTML` is meant as a replacement for `innerHTML`. In the use case you describe, you would have never wanted `innerHTML` anyway. You'd want `innerText` or `textContent`.
But that's what setHTML isn't at all a replacement for innerHTML.
You still need innerHTML when you want to inject HTML tags in the page, and you could already use innerText when you didn't want to.
Having something in between is seriously useless.
> You still need innerHTML when you want to inject HTML tags in the page
What makes you say this?
> If the default configuration of setHTML( ) is too strict (or not strict enough) for a given use case, developers can provide a custom configuration that defines which HTML elements and attributes should be kept or removed.
Injecting markup into someone else's website isn't what I'd call too strict a default configuration
If you mean to convey that it's possible to configure it to filter properly, let me introduce you to `textContent` which is older than Firefox (I'm struggling to find a date it's so old)
That's the whole point of the setHTML.
How would I set a header level using textContent?
The traditional way: separating data and code
If you allow <h1> in the setHTML configuration or use the default, users with the tag in their username also always get it rendered as markupIt sounds like you're arguing against a specific usecase, rather than the technology itself. If you don't want arbitrary markup in usernames, setHTML would absolutely be the wrong choice, but that's not really a good argument against setHTML.
Which is why you only use it where you want to allow some kind of html..?
> but this still allows arbitrary markup to the page (even <style> CSS rules) if I'm reading the docs correctly.
If that's true, seems like it's still a security risk given what you can do with CSS these days: https://news.ycombinator.com/item?id=47132102
You can use selectors to gain some information about things like input fields, e.g. https://www.invicti.com/blog/web-security/private-data-stole...
Or I guess you could completely restyle and change the text of UI elements so it looks like the user is doing one thing when they're actually doing something completely different like sending you money
Back in 2002 (?) I got banned from a certain auction site because I managed to inject HTML into my username that made it so once I had bid the "Bid" button disappeared for all subsequent users.
If I'm reading this right,
will strip all elements out. That's not too difficult.Plus this is defense-in-depth. Backends will still need to sanitize usernames on some standard anyhow (there's not a lot of systems out there that should take arbitrary Unicode input as usernames), and backends SHOULD (in the RFC sense [1]) still HTML-escape anything they output that they don't want to be raw HTML.
[1]: https://www.rfc-editor.org/rfc/rfc2119
You aren't reading it right.
This Sanitizer will allow everything by default, but setHTML will still block elements/attributes that can lead to XSS.You might want something like:
This will replace <h1> elements with their children (i.e. text in this case), but disallow all other elements and attributes.i think the use case for setHTML is for user content that contains rich text and to display that safely. so this is not an alternative for escaping text or inserting text into the DOM but rather a method for displaying rich text. for example maybe you have an editor that produces em, and strong tags so now you can just whitelist those tags and use setHTML to safely put that rich text into the DOM without worrying about all the possible HTML parsing edge cases.
> Who would ever want this?
Your lack of imagination is disturbing :-)
https://github.com/lelanthran/ZjsComponent
> So you can still inject <h1> or <br><br><br>... etc into your username, in the given example
How exactly, given that setHTML sanitizes the input? If you don't want to have any HTML tags allowed, seems you can configure that already? https://wicg.github.io/sanitizer-api/#built-in-safe-default-...
> How exactly, given that setHTML sanitizes the input?
The article says that the output is:
So it keeps (non-script) html tags (and presumably also attributes) in the input. Idk how you're asking "how" since it's the default behaviorStripping HTML tags completely has always been possible with the drop-in replacement `textContent`. Making a custom configuration object for that is much more roundabout
Yes, because that's the default configuration, if you don't want that, stop using the default configuration? It's still sanitizing away the common XSS holes, hence it's a safer alternative to .innerHTML, and a more flexible alternative to .innerText
Shouldn't use innerText anyway (nonstandard, worse performance, tries to parse the HTML and gives you unexpected behavior if e.g. a style is set that makes an element invisible but still has text inside, doesn't work on all DOM nodes...)
I can see how it's a way of allowing some tags like bold and italic without needing a library or some custom parser, but I didn't understand what the point of this default could be and so why it exists (a sibling comment proposed a plausible answer: hardening on top of another solution)
> Yes, because that's the default configuration, if you don't want that, stop using the default configuration?
"don't use it if it's not what you want" is perhaps the silliest possible answer to the question "what's the use-case for this"
> Shouldn't use innerText anyway (nonstandard, worse performance, tries to parse the HTML and gives you unexpected behavior if e.g. a style is set that makes an element invisible but still has text inside, doesn't work on all DOM nodes...)
Maybe you meant .innerHTML? .innerText AFAIK doesn't try to parse HTML (why would it?), but I don't understand what you mean with nonstandard, both .innerHTML and .innerText are part of the standards, and I think they've been for a long time.
> but I didn't understand what the point of this default could be and so why it exists (a sibling comment proposed a plausible answer: hardening on top of another solution) [...] the question "what's the use-case for this"
I guess maybe third time could be the charm: it's for preventing XSS holes that are very common when people use .innerHTML
> maybe third time could be the charm: it's for preventing XSS holes
That information is in the question, so sadly no this still doesn't make sense to me because I don't understand any scenario in which this is what the developer wants. You always still need more code (to filter the right tags) or can just use textContent (separating data and code completely, imo the recommended solution)
> Maybe you meant .innerHTML? .innerText AFAIK doesn't try to parse HTML (why would it?)
No, I didn't mean that, yes it does, and no I don't know why it is this way. If you don't believe me and don't want to check it out for yourself, I'm not sure what more I can say
> I don't understand any scenario in which this is what the developer wants.
Client-side includes.
It seems like the goal of the default configuration is preventing script injection while being otherwise very permissive. Basically, "safer than innerHTML, even when used very lazily". But I would expect guidance to evolve saying that it almost never makes sense to use the default and instead to specify a configuration that makes contextual sense for a given field.
The default might be suitable for something like an internal blog where you want to allow people to sometimes go crazy with `<style>` tags etc, just not inject scripts, but I would expect it to almost always make sense to define a specific allowed tag and attribute list, as is usually done with the userland predecessors to this API.
There’s innerText if you don’t want markup. Or more verbosely, document.createTextNode followed by whatever.appendChild.
> Who would ever want this?
Anyone who wants to provide some level of flexibility but within bounds. Say, you want to allow <strong> and <em> in a forum post but not <script>. It's not too difficult to imagine uses.
Forums would already have code that sanitizes user input when it's submitted. Users aren't directly setting html elements.
And is that sanitization perfect? Kept up to date?
With a safe API like this one that's tied to the browser's own interpretation of HTML (i.e. it is perfectly placed to know exactly what is and isn't dangerous given it is the one rendering it) wouldn't it be much better to rely on that?
> So you can still inject <h1> or <br><br><br>... etc into your username
Are we taking out all the fun of the web? I absolutely loved the <marquee> names people had in the early days of Facebook, it was all harmless fun.
If injection of frontend code takes down your backend, your backend sucks, fix it.
What I really want is a <sandbox> element that can safely run dangerous code, not something that modifies dangerous code.
Iframes have significant restrictions as they can’t flow with the DOM. With AI and the increase in dynamic content, there’s going to be even more situations where you run untrusted code. I want configurable encapsulation.
Title was a bit rage-baity. And I think you can already do sanitation by writing a function to check input before passing it to innerHTML?
This really just seems like another attempt at reinventing the wheel. Somewhat related, I find it ironic how i cannot browse hacks.mozilla.org in my old version of firefox("Browser not supported"). Also, developer.mozilla.org loads mangled to various degrees in current versions of palemoon, basilisk, and seamonkey
It's like there is some sort of "browser cartel" trying to screw up The Web.
> you can already do sanitation by writing a function to check input before passing it to innerHTML
This is like saying C is memory safe as long as your code doesn't have any bugs.
More saliently, it does not consider parser differentials.
Seems like this has a bunch of footguns. Particularly if you interact with the Sanitizer api, and particularly if you use the "remove" sanitizer api.
Don't get me wrong, better than nothing, but also really really consider just using "setText" instead and never allow the user to add any sort of HTML too the document.
> never allow the user to add any sort of HTML too the document.
What about when the author of the page wants to add large html fragments to the page?
Are you saying that you cannot think of a single use for this, considering how often innerHTML is being used?
Using an allowlist based Sanitizer you are definitely less likely to shoot yourself in the foot, but as long as you use setHTML you can't introduce XSS at least.
It's worse than nothing, since inevitably people will use this thinking it's 100% safe when it's not.
And for those who want a better innerHTML, use insertAdjacentHTML https://developer.mozilla.org/en-US/docs/Web/API/Element/ins...
I don’t ever use it with user input, but use it often when building SPA without frameworks
This is nice. The best part is that all aspects of network access are now properly controlled so that security transitioned from a chain of trusted code to a chain of trusted security setup on hosts, with existing workable safe defaults.
naming the old behavior setHTMLUnsafe is what did it for me. security features that require developers to opt in don't work. making the unsafe path feel unsafe does.
Well, the name SetHTML, or let's say:
Makes objectively more sense than: It is a fairly small thing, but ... really. One day someone should clean up the mess that is JavaScript. Guess it will never happen, but JavaScript has so many strange things ...I understand that this here is about protection against attacks rather than a better API design, but really - APIs should ideally be as great as possible the moment they are introduced and shown to the public.
To be pedantic that’s the DOM API, which is exposed to JavaScript.
The DOM API has always felt like, and still does, it was written by people that have never made an API.
I don't think that's pedantic. Seems like a valid objection to me.
So many issues in the client JS world originate from insufficient or bad browser APIs.
I don’t really think it’s pedantic it’s just that unless you preface a lot of comments on HN these days, you’ll get a lot of whataboutism and straw man arguments.
Tangential but it's amazing in 2026 browsers still don't ship a native DOM morph/merge API like morphdom or idiomorph.
Kids in the '90s:
Kids in the '20s:Kids in the '30s:
Prompt injection is just the same problem on a new technology. We didn't learn anything from the 90s.Another solution is just use this at the start of your code:
Then assignments to innerHTML do not modify the element's textContent or child node list and assignments to it will not throw an error.is there any situation where innerHTML would be preferable? I could suppose it might be more performant and so if you were constructing something that was not open to XSS it might theoretically be better (with the usual caveat that people always make mistakes about this kind of thing)
at what point can we consider the development of "set this element's text/html" to be done?
When browsers implement a variant that lets you separate data and code perhaps. That's what I expected when reading the headline: setHtml(code, data, data, ...), just like parameterised SQL works: prepare("select rowid from %s where time < %n", tablename, mynumber)
This new method they've cooked up would be called eval(code,options) if html was anything other than a markup language
tablenames cannot be parameterized in SQL
https://stackoverflow.com/questions/78516750/parametrize-tab...
A rather deceptive title, given that 'innerHTML' isn't going away.
I think the title is trying to convince you to switch from InnerHTML to SetHTML.
Nice one. Will there be any impact on __dangerouslySetInnerHTML (React)?
Oh, that's nice-to-have. Good work, Mozilla.
It would close the loop better if you could also use policy to switch off innerHTML in a given page, but definitely a step in the right direction for plain-JavaScript applications.
My corporate firewall blocks it due to the "hacks" in the subdomain / url. This is silly.
That's why the DNS for hackernews is news.ycombinator.com and not hackernews.org