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Handle inline scripts when systemjs itself is inline #2369

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Handle inline scripts when systemjs itself is inline #2369

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dmail
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@dmail dmail commented Nov 2, 2021

Description

When systemjs is inlined in the HMTL file, it won't execute inline scripts

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf8" />
    <link rel="icon" href="data:," />
    <script>
      // Here goes systemjs/dist/s.js inlined
    </script>
  </head>
  <body>
    <script>
      System.register([], function () {
        "use strict"

        return {
          execute: function () {
            alert("executed") // -> not executed by systemjs
          },
        }
      })
    </script>
  </body>
</html>

This pull request should fix this use case, it is a follow up of #2357

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github-actions bot commented Nov 2, 2021 •
edited

File size impact

Merging main into main will impact 2 files in 1 group.

browser (2/2)
File raw gzip brotli Event
dist/s.min.js +61 (7,661) +38 (3,030) +37 (2,749) modified
dist/system.min.js +61 (11,950) +36 (4,613) +31 (4,155) modified
Total size impact +122 (19,611) +74 (7,643) +68 (6,904)
node (0/1)

No impact on files in node group.

extras (0/8)

No impact on files in extras group.

Generated by file size impact during size-impact#1526193853

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dmail commented Nov 2, 2021 •
edited

Sorry the commit is incorrect will push the right commit shortly

Done

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dmail commented Nov 9, 2021 •
edited

The build failed but it seems unrelated, I think it would pass if restarted but I don't have the rights to restart the Travis build.

joeldenning
joeldenning reviewed Nov 9, 2021
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This looks pretty good to me. Can you think of a way to add tests? Seems to be hard since the tests are all run in the same HTML file that loads systemjs via <script src> rather than inline.

The lastScript logic that's already present in systemjs doesn't seem to be the best approach, since multiple inline scripts would have the same lastAutoImportUrl logic in them. Using document.currentScript would be better, but isn't supported in IE11. I wonder if we could use document.scripts[document.scripts.length - 1] rather than the current approach? Got that idea from https://makandracards.com/makandra/497684-emulating-document-currentscript-in-old-browsers. If we can switch to that, I think it would be better.

src/features/script-load.js Outdated
}
else {
inlineScriptCount++
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Suggested change
inlineScriptCount++
inlineScriptCount++;

src/features/script-load.js Outdated
systemJSPrototype.register = function (deps, declare) {
if (hasDocument && document.readyState === 'loading' && typeof deps !== 'string') {
var scripts = document.querySelectorAll('script[src]');
var lastScript = scripts[scripts.length - 1];
var lastAutoImportUrl;
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Why did you move this inside of register? To avoid race conditions with multiple scripts being executed in the same tick of the event loop? I didn't think it would be possible for two inline scripts to execute before a setTimeout tick occurs.

src/features/script-load.js Outdated
systemJSPrototype.register = function (deps, declare) {
if (hasDocument && document.readyState === 'loading' && typeof deps !== 'string') {
var scripts = document.querySelectorAll('script[src]');
var lastScript = scripts[scripts.length - 1];
var lastAutoImportUrl;
lastAutoImportDeps = deps;
if (lastScript) {
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I think the ideal implementation would use the src if it's present and the __inline_script__ if it's not. Something like this:

Suggested change
if (lastScript) {
if (lastScript.src) {

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dmail commented Nov 15, 2021

Thanks for the review, for now I don't have time to handle your feedback but I'll come back to this PR when possible ;)

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dmail commented Dec 1, 2021

I have just pushed a commit to address the review.

About how to test this scenario where systemjs itself is inlined:
I don't know how I could do it properly with the test tools you have in place.
However if I can introduce playwright I know how I could do it:

  • start a static file server injecting systemjs inline into html
  • launch a chrome headless using playwright
  • write an html page reproducing what we want to test (systemjs inline + an inline System.register)
  • make chrome navigate to this html page and assert the file is properly executed

But I would like your approval about this strategy before writing it.

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@dmail @joeldenning