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Test if ES6 is ~fully supported
var supportsES6 = function() {
try {
new Function("(a = 0) => a");
return true;
catch (err) {
return false;
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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.

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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?

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triblondon commented Aug 26, 2016

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

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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).

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kenberkeley commented Mar 1, 2019

  if (typeof Symbol === 'undefined') {
    document.write('<script crossorigin="anonymous" src=",es7&flags=gated"><\/script>')

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