bendc/supportsES6.js

Created August 25, 2016 08:05

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Test if ES6 is ~fully supported

Raw

supportsES6.js

	var supportsES6 = function() {
	try {
	new Function("(a = 0) => a");
	return true;
	}
	catch (err) {
	return false;
	}
	}();

Author

bendc commented Aug 25, 2016

Load your untranspiled ES6 file for modern browsers:

if (supportsES6) {
  var script = document.createElement("script");
  script.src = "my-es6-file.js";
  document.head.appendChild(script);
}

rik commented Aug 25, 2016

I think this requires some performance testing since you can't benefit from browsers "parse ahead" behaviour to download the JS file as soon as possible.

triblondon commented Aug 26, 2016

The ~ is pretty critical here, unless we know that for every browser, the last part of ES6 to be supported was either arrows or default args?

triblondon commented Aug 26, 2016

@rik optimising for the modern browsers, you could <link rel=preload> it

Author

bendc commented Aug 26, 2016

@triblondon Yup, the critical test is the a = 0 (all browsers supporting default parameters have a fairly complete support of ES6 -- for example, Edge 13 will be rejected by this test despite a decent ES6 coverage).

kenberkeley commented Mar 1, 2019 •

edited

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<html>
<head>
  <script>
  if (typeof Symbol === 'undefined') {
    document.write('<script crossorigin="anonymous" src="https://polyfill.io/v3/polyfill.min.js?features=es6,es7&flags=gated"><\/script>')
  }
  </script>
</head>
<body>
</body>
</html>

cai-zhuo commented Mar 6, 2023 •

edited

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@triblondon Yup, the critical test is the a = 0 (all browsers supporting default parameters have a fairly complete support of ES6 -- for example, Edge 13 will be rejected by this test despite a decent ES6 coverage).

I wanna know how to prove “all browsers supporting default parameters have a fairly complete support of ES6”
Thankfully， if you can show links or refs

vlakoff commented May 15, 2025 •

edited

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MediaWiki previously used this snippet and is now updating it to also test for these ES2017 features:

Trailing commas in function parameters
Async functions

See the update in patchset 1141401.

Ensuring ES2015 (ES6) grammar and syntax support:

new Function( '(a = 0) => a' );

Ensuring ES2017 (ES8) grammar and syntax support:

new Function( 'async (a = 0,) => a' );

The crucial test is the one for trailing commas, as it was the last ES2017 feature to be implemented (for instance, in Chrome 58).
You can find more details in the "Feature summary" table at the end of this Feature support list on caniuse.com.

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