A way to stream content into an element

Use-case: I work on a news site and I want to create visual transitions between articles, but I don't want to lose the benefits of streaming. So:

User clicks on link
Create a new article element to contain the incoming article
Start fetching content
Pipe content into new article element
Begin the visual transition once elements appear in the new article element

Not only is innerHTML is slower way to do this (due to a lack of streaming), it also introduces a number of behavioural differences. It'd be great to try to limit these, eg allow inline scripts to execute before additional elements are inserted.

Parts of this can be hacked using document.write and <iframe>, but it'd be good to have a non-hacky way.

Code for the above use-case if element.writable provided a way to stream HTML into the element.

const article = document.createElement('article');
const response = await fetch('article.include');
const articleHasContent = new Promise(resolve => {
  const observer = new MutationObserver(() => {
    observer.disconnect();
    resolve();
  });
  observer.observe(article, {childList: true});
});

response.body
  .pipeThrough(new TextDecoder())
  .pipeTo(article.writable);

await articleHasContent;
performTransition();

There is also https://w3c.github.io/DOM-Parsing/#idl-def-range-createcontextualfragment(domstring) which does execute scripts (when inserted into a document). As a possible alternative to document.write in the meantime...

TIL! I guess you mean an alternative to innerHTML?

No, as an alternative to document.write in your hack. Don't even need an iframe, just a Range instance.

http://software.hixie.ch/utilities/js/live-dom-viewer/saved/4716

@zcorpan

@zcorpan ah, that doesn't allow partial trees http://software.hixie.ch/utilities/js/live-dom-viewer/?saved=4717, which you kinda need if you're trying to stream something like an article.

Hello! I'm curious about the possibility to insert scripts.

I'm trying to execute an script and I see the script is executed after insertion.

<!DOCTYPE html>
<body>
<script>
var r = new Range();
// Write some more content - this should be done async:
document.body.appendChild(r.createContextualFragment('<p>hello'));
document.body.appendChild(r.createContextualFragment(' world</p>'));
document.body.appendChild(r.createContextualFragment('<script>console.log("yeap");<\/script>'));
// done!!
</script>
</body>

I've two questions:
What about if the inserted script has the flag... async or defer? Those flags will not have effect.

Will you keep this function in the standard? Or are you planning to remove it?

Finally I found (you gave me) the best way to insert content to the document.Thanks a lot!

@rianby64

@rianby64 note that the example above creates two paragraphs rather than one.

What about if the inserted script has the flag... async or defer? Those flags will not have effect.

The scripts will be async, as if you'd created them with document.createElement('script'). For the streaming solution I mentioned in the OP, I'd like the parser to queue DOM modifications while a non-async/defer script downloads and executes, but allow something like a look-ahead parser.

Will you keep this function in the standars?

Which function? createContextualFragment? I don't see why it'd be removed.

OK. Thanks a lot again.

ah, that doesn't allow partial trees

Indeed.

@jakearchibald

In general I think we want to be able to provide ReadableStream or Response objects to APIs that currently take a URL. @jakearchibald, would something that let you assign a ReadableStream or Response (backed by a stream) to an iframe.src satisfy your use case?

The key part here is to not have to use a separate iframe plus adoption of the current parser insertion point into a different document. Instead, we just want to parse into an existing document location.

This means creating an element that has the concept of partially loaded state, right? An iframe already has all of that, but do other html container elements? So wouldn't we need to create something that has all the load event, error event, and other stateful information of an iframe? Or maybe all that exists today. HTML always catches me out.

@wanderview

@wanderview

This means creating an element that has the concept of partially loaded state, right?

I think we can get away without this. If an element has a writable endpoint you'll get locking on that writable for free. However, during streaming you'll be able to modify the children of the element, even set the element's innerHTML. The HTML parser already has to deal with this during page load, so I don't think we need to do anything different.

So wouldn't we need to create something that has all the load event, error event, and other stateful information of an iframe?

We probably don't need this either. htmlStream.pipeTo(div.writable) - since pipeTo already returns a promise you can use that for success/failure info.

How would this interact / compare with the following scenario:

Rather than fetching HTML snippets from the server, I'm much more likely to be able to fetch [we'll assume newline-delimited to enable stream parsing] a minimal JSON encoding of whatever entity I'm trying to display.

Partially, this is just down to the fact that most web servers wrap HTML output in a series of filters, one of which is a base "<html><head/><body>...</body></html>" template. Obviously, that can [easily, from a purely technical perspective] change, but spitting out independent <div>s is going to take some cultural change on the server side. JSON we have today, and won't take any convincing.

... so, assuming that we use JSON, Is there a performance win to being able to render JSON snippets [as they come over the network] to HTML? The trade-off I'd assume we're making is on triggering additional layouts; put another way, is it faster to do:

[ JSON blob representing n divs ]: JSON -> HTML -> DOM in one step -or-
[ streaming JSON blob representing n divs ]: while (nextJSONitem) { JSON -> HTML -> DOM }

My expectation is that the answer is "it depends"; I don't have a sufficiently reliable playground for testing this to any degree of accuracy, but I would expect we'd want to keep the render pipeline as unobtrusive as possible while minimizing network->screen latency for individual items, using the following as trade-offs:

time to render & re-compute layout for:
- each items in an array individually vs
- all items in an array as a single DOM manipulation vs
- batches of items
total time to:
- fetch all items
- pull a single item out of a streaming JSON blob

... ideally all while minimizing client complexity ("they wrote a lot of code to make things that slow"). Thankfully that part should be hidden in frameworks.

... OR am I totally barking up the wrong tree with the idea that JSON is the right delivery mechanism, and we should aim to generate server-side HTML snippets for pretty much anything that can be fetched-with-latency?

Implement streamAppendHTMLUnsafe

Bug 1998582 [wpt PR 55887] - Implement streamAppendHTMLUnsafe, a=test…

In #11964 we had consensus to advance this proposal to stage 2, with the specific scope of adding streamHTMLUnsafe() and adding the runScripts option to both streamHTMLUnsafe() and setHTMLUnsafe().

Are there any updates on the stream*() APIs? We have need of them in several products and aren't keen to wait for the declarative patching work.

Are there any updates on the stream*() APIs? We have need of them in several products and aren't keen to wait for the declarative patching work.

Those dont depend on each other. The stream* work is stage 2 and ready to be played with behind a flag in chrome canary. Happy for feedback on that!

b2: v148/renewed-html-insertion-streaming-methods contract + page ids

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A way to stream content into an element #2142

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A way to stream content into an element #2142

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jakearchibald commented on Dec 7, 2016

zcorpan commented on Dec 7, 2016

jakearchibald commented on Dec 7, 2016

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rianby64 commented on Dec 7, 2016

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