Exclude core-js polyfills from ESM-capable browser bundles#6068
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**Why**: So that the majority of users don't have to pay the performance penalty for polyfills supporting legacy browsers, avoid loading those polyfills except in the legacy browsers.
…r modern browsers
aduth
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Mar 15, 2022
| @@ -1,8 +1,7 @@ | |||
| import 'promise-polyfill/src/polyfill'; | |||
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core-js includes a Promise and URL polyfill, so we don't need the other one. Which is nice because it lets us use fewer dependencies.
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Based on failing build, looks like I need to fix something with how the regenerator runtime is included for modern browser builds. |
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…#6075) * Revert "Revert "Exclude core-js polyfills from ESM-capable browser bundles (#6068)" (#6074)" This reverts commit 376bc2c. * Drop jsbundling_rails in favor of custom rake task **Why**: So that we can have CI install dependencies in the same way as is expected in production, since jsbundling_rails will always install devDependencies with no option to opt-out. * Revert "Drop jsbundling_rails in favor of custom rake task" This reverts commit c4b97b5. * Use NODE_ENV production to exclude devDependencies in CI * Move babel-plugin-polyfill-corejs3 to dependencies **Why**: So that it's available in production build environments. changelog: Improvements, Optimization, Skip polyfill load behavior for modern browsers
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**Why**: - Because polyfills are intended to be confined to the polyfill package (#6060) - So that it's not included in modern browsers (#6068, -0.9kb gzipped) - To reduce surface area of dependencies shared with USWDS (related to 18F/identity-design-system#312 (comment)) changelog: Internal, Optimization, Reduce size of JavaScript for modern browsers
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**Why**: - Because polyfills are intended to be confined to the polyfill package (#6060) - So that it's not included in modern browsers (#6068, -0.9kb gzipped) - To reduce surface area of dependencies shared with USWDS (related to 18F/identity-design-system#312 (comment)) changelog: Internal, Optimization, Reduce size of JavaScript for modern browsers
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Why: So that the majority of users don't have to pay the performance penalty for polyfills supporting legacy browsers, avoid loading those polyfills except in the legacy browsers.
This builds on #6060 (#6060 (comment)). While #6060 excluded polyfills implemented through our
@18f/identity-polyfillpackage, it did not cover polyfills injected through Babel's@babel/preset-envpreset. With these changes,@babel/preset-envis configured to only include polyfills for browsers which are capable of ESM, and includes a full set of polyfills for non-ESM-capable browsers in@18f/identity-polyfill, to be loaded only for those browsers. JavaScript syntax is still downgraded to all supported browsers including IE11, which is also tested for usingyarn es5-safe.Local measurements (via
NODE_ENV=production make run) show a reduction of JavaScript on the home page of ~34% (80.3kb to 53.2kb).