Proposal: to add a noblock type to script tags

[ahmedHusseinF]

Currently we have 3 types of including scripts in an html page:

• Block HTML parsing by fetching and executing with just a plain script tag
• Fetch the script in parallel to parsing HTML but block once downloaded to start execution (async)
• Fetch the script in parallel to parsing HTML and start execution after the HTML finishes parsing (defer)

But sometimes I have huge JavaScript files that has nothing to do with the DOM and it is either blocking HTML parsing or waiting.

This proposal propose adding an option to download and parse and execute JavaScript in parallel to HTML parsing by adding a specific option on the script tag and this can let me mangle with just JavaScript code as long as my script doesn't touch the DOM.

This is my first time making a big open source contribution, so I am open to any critique or directing me in the correct direction if this doesn't look good.

[domenic]

This use case makes sense, but we already have a mechanism to support this: web workers. In other words, instead of

<script type=noblock src="foo.js"></script>

you'd do

<script>new Worker("foo.js");</script>

In my opinion the latter (existing) solution is clearer and more explicit. The noblock version is a bit weird, because it's strange to include a script via a script tag and have that script not operate in the same JS realm as the document.

[ahmedHusseinF]

Thanks for replying quickly.

Actually I can see the workers covering at least half of the use cases but what I meant was including this big JS file and for example attaching it to window within the same page event loop.

<script type=noblock src="foo.js" onload="fooLoaded(event)"></script>
<script>
  function fooLoaded(loadEv){
    window.foo.whatever();
  }
</script>

I get this can be implemented with dynamic import and window.onload but this will have the edge as the script has fully been parsed and executed in parallel to HTML parsing in particular if I am relying on this to get my page to first render.

For example the runtime of angular abstracted without DOM access which can get quite big.

[domenic]

We can't allow access to window without allowing access to the DOM, because the window is a critical part of the DOM. That's why workers have their own separate global object.

[rniwa]

Yeah, we can't do this. You're either in a worker or in the main thread (same thread as the rest of the DOM). DOM isn't thread safe / threadable.

[annevk]

@ahmedHusseinF what kind of functionality do you want to access on window "in parallel" that isn't in workers?