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ebidel/feature_detect_es_modules.js

Last active September 4, 2023 13:56
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Feature detect ES modules: both static import and dynamic import()
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feature_detect_es_modules.js
<!--
Complete feature detection for ES modules. Covers:
1. Static import: import * from './foo.js';
2. Dynamic import(): import('./foo.js').then(module => {...});
Demo: http://jsbin.com/tilisaledu/1/edit?html,output
Thanks to @_gsathya, @kevincennis, @rauschma, @malyw for the help.
-->
<body></body>
<!-- Remember: static modules have a fallback! -->
<script type="module">
console.log('This browser supports <script type="module">');
</script>
<script nomodule>
console.log('This browser DOES NOT support <script type="module">');
</script>
<script>
// Feature detect static imports.
function supportsStaticImport() {
const script = document.createElement('script');
return 'noModule' in script;
}
// Feature detect dynamic import().
function supportsDynamicImport() {
try {
new Function('import("")');
return true;
} catch (err) {
return false;
}
}
// Usage.
let el = document.createElement('pre');
el.textContent = `
Supports ES module static import: ${supportsStaticImport()}
Supports dynamic ES module import(): ${supportsDynamicImport()}
`
document.body.appendChild(el);
</script>
@rugk
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rugk commented Feb 20, 2020

Does anyone have an idea how a "loader" type library can feature detect dynamic import so it could dynamically load an ES Module implementation, without assuming anything from the embedding app (no requirement for bundler transforms, CSP changes, etc).

A perfect case for Stackoverflow, I've asked it there: How to feature-detect whether a browser supports dynamic ES6 module loading?

@Mouvedia
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Mouvedia commented Feb 3, 2021 •
edited
Loading

console.log('This browser DOES NOT support <script type="module">');

This is wrong.
e.g. Safari 10.1 supports type="module" but not the nomodule attribute
see https://gist.github.com/samthor/64b114e4a4f539915a95b91ffd340acc

@erikt9
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erikt9 commented Dec 7, 2021

A more concise supportsStaticImport script:

function supportsStaticImport() {
    return 'noModule' in HTMLScriptElement.prototype;
}

@rugk
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rugk commented Dec 8, 2021 •
edited
Loading

@erikt9 feel free to submit this as an answer to the Stackoverflow question linked above.

@mindhells
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https://developer.mozilla.org/en-US/docs/Web/API/HTMLScriptElement

function checkModuleSupport() {
  if ('supports' in HTMLScriptElement) {
    return HTMLScriptElement.supports('module');
  }
  return 'noModule' in document.createElement('script');
}

@rugk
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rugk commented Mar 18, 2022

@mindhells you feel also free to submit this as an answer to the Stackoverflow question linked above.

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