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Stuck on an issue?

Lightrun Answers was designed to reduce the constant googling that comes with debugging 3rd party libraries. It collects links to all the places you might be looking at while hunting down a tough bug.

And, if you’re still stuck at the end, we’re happy to hop on a call to see how we can help out.

For legacy-javascript advice, suggest excluding some polyfills for "modern" build

See original GitHub issue

As of today, @babel/preset-env + esmodules: true + bugfixes: true will apply these polyfills and transforms:

Using targets:
{
  "android": "61",
  "chrome": "61",
  "edge": "16",
  "firefox": "60",
  "ios": "10.3",
  "opera": "48",
  "safari": "10.1",
  "samsung": "8.2"
}

Using modules transform: auto

Using plugins:
  proposal-nullish-coalescing-operator { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  proposal-optional-chaining { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  proposal-json-strings { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  proposal-optional-catch-binding { "android":"61", "chrome":"61", "edge":"16", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  proposal-async-generator-functions { "android":"61", "chrome":"61", "edge":"16", "ios":"10.3", "opera":"48", "safari":"10.1" }
  proposal-object-rest-spread { "edge":"16", "ios":"10.3", "safari":"10.1" }
  transform-dotall-regex { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1" }
  proposal-unicode-property-regex { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  transform-named-capturing-groups-regex { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  transform-unicode-regex { "ios":"10.3", "safari":"10.1" }
  bugfix/transform-async-arrows-in-class { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  bugfix/transform-edge-default-parameters { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  bugfix/transform-edge-function-name { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  bugfix/transform-safari-block-shadowing { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  bugfix/transform-safari-for-shadowing { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  bugfix/transform-tagged-template-caching { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  transform-modules-commonjs { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  proposal-dynamic-import { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }

Using polyfills with `entry` option:

[/Users/cjamcl/src/lighthouse/lighthouse-core/scripts/legacy-javascript/variants/655dfce5bd8bbca5337615b71d06458d12bc2665e1a2c9e4e760d4bfef5691f4/core-js-3-preset-env-esmodules/true-and-bugfixes/main.js] Replaced core-js entries with the following polyfills:
  es.symbol.description { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  es.symbol.async-iterator { "android":"61", "chrome":"61", "edge":"16", "ios":"10.3", "opera":"48", "safari":"10.1" }
  es.symbol.match { "edge":"16" }
  es.symbol.replace { "edge":"16" }
  es.symbol.search { "edge":"16" }
  es.symbol.split { "edge":"16" }
  es.array.flat { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  es.array.flat-map { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  es.array.index-of { "ios":"10.3", "safari":"10.1" }
  es.array.iterator { "android":"61", "chrome":"61", "opera":"48", "samsung":"8.2" }
  es.array.last-index-of { "ios":"10.3", "safari":"10.1" }
  es.array.reverse { "ios":"10.3", "safari":"10.1" }
  es.array.slice { "ios":"10.3", "safari":"10.1" }
  es.array.sort { "android":"61", "chrome":"61", "ios":"10.3", "opera":"48", "safari":"10.1" }
  es.array.splice { "ios":"10.3", "safari":"10.1" }
  es.array.unscopables.flat { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  es.array.unscopables.flat-map { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  es.array-buffer.constructor { "ios":"10.3", "safari":"10.1" }
  es.array-buffer.slice { "ios":"10.3", "safari":"10.1" }
  es.math.hypot { "android":"61", "chrome":"61", "opera":"48", "samsung":"8.2" }
  es.number.parse-float { "ios":"10.3", "safari":"10.1" }
  es.number.to-fixed { "edge":"16" }
  es.object.assign { "edge":"16" }
  es.object.define-getter { "android":"61", "chrome":"61", "opera":"48" }
  es.object.define-setter { "android":"61", "chrome":"61", "opera":"48" }
  es.object.from-entries { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  es.object.lookup-getter { "android":"61", "chrome":"61", "opera":"48" }
  es.object.lookup-setter { "android":"61", "chrome":"61", "opera":"48" }
  es.promise { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  es.promise.finally { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  es.reflect.set { "edge":"16" }
  es.regexp.constructor { "edge":"16" }
  es.regexp.flags { "edge":"16" }
  es.regexp.to-string { "edge":"16" }
  es.string.ends-with { "edge":"16" }
  es.string.includes { "edge":"16" }
  es.string.match { "edge":"16" }
  es.string.pad-end { "ios":"10.3", "safari":"10.1" }
  es.string.pad-start { "ios":"10.3", "safari":"10.1" }
  es.string.replace { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  es.string.search { "edge":"16" }
  es.string.split { "edge":"16" }
  es.string.starts-with { "edge":"16" }
  es.string.trim { "ios":"10.3", "safari":"10.1" }
  es.string.trim-end { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  es.string.trim-start { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  es.typed-array.float32-array { "ios":"10.3", "safari":"10.1" }
  es.typed-array.float64-array { "ios":"10.3", "safari":"10.1" }
  es.typed-array.int8-array { "ios":"10.3", "safari":"10.1" }
  es.typed-array.int16-array { "ios":"10.3", "safari":"10.1" }
  es.typed-array.int32-array { "ios":"10.3", "safari":"10.1" }
  es.typed-array.uint8-array { "ios":"10.3", "safari":"10.1" }
  es.typed-array.uint8-clamped-array { "ios":"10.3", "safari":"10.1" }
  es.typed-array.uint16-array { "ios":"10.3", "safari":"10.1" }
  es.typed-array.uint32-array { "ios":"10.3", "safari":"10.1" }
  es.typed-array.from { "ios":"10.3", "safari":"10.1" }
  es.typed-array.of { "ios":"10.3", "safari":"10.1" }
  es.typed-array.to-locale-string { "edge":"16" }
  esnext.aggregate-error { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.array.last-index { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.array.last-item { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.composite-key { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.composite-symbol { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.global-this { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.map.delete-all { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.map.every { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.map.filter { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.map.find { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.map.find-key { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.map.from { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.map.group-by { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.map.includes { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.map.key-by { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.map.key-of { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.map.map-keys { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.map.map-values { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.map.merge { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.map.of { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.map.reduce { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.map.some { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.map.update { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.math.clamp { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.math.deg-per-rad { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.math.degrees { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.math.fscale { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.math.iaddh { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.math.imulh { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.math.isubh { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.math.rad-per-deg { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.math.radians { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.math.scale { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.math.seeded-prng { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.math.signbit { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.math.umulh { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.number.from-string { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.observable { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.promise.all-settled { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.promise.any { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.promise.try { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.reflect.define-metadata { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.reflect.delete-metadata { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.reflect.get-metadata { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.reflect.get-metadata-keys { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.reflect.get-own-metadata { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.reflect.get-own-metadata-keys { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.reflect.has-metadata { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.reflect.has-own-metadata { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.reflect.metadata { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.set.add-all { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.set.delete-all { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.set.difference { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.set.every { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.set.filter { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.set.find { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.set.from { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.set.intersection { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.set.is-disjoint-from { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.set.is-subset-of { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.set.is-superset-of { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.set.join { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.set.map { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.set.of { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.set.reduce { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.set.some { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.set.symmetric-difference { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.set.union { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.string.at { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.string.code-points { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.string.match-all { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.string.replace-all { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.symbol.dispose { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.symbol.observable { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.symbol.pattern-match { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.weak-map.delete-all { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.weak-map.from { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.weak-map.of { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.weak-set.add-all { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.weak-set.delete-all { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.weak-set.from { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  esnext.weak-set.of { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  web.dom-collections.iterator { "android":"61", "chrome":"61", "edge":"16", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  web.immediate { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  web.queue-microtask { "android":"61", "chrome":"61", "edge":"16", "firefox":"60", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  web.url { "android":"61", "chrome":"61", "edge":"16", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  web.url.to-json { "android":"61", "chrome":"61", "edge":"16", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }
  web.url-search-params { "android":"61", "chrome":"61", "edge":"16", "ios":"10.3", "opera":"48", "safari":"10.1", "samsung":"8.2" }

That means, if you follow our planned module/nomodule strategy, the modern bundle will still ship Promise and TypedArrays.

Polyfilling just the typed-arrays and Promise is about 85KB:

// bundle and minify this file -> ~85kB
require("../../../../node_modules/core-js/modules/es.promise");
require("../../../../node_modules/core-js/modules/es.typed-array.float32-array");
require("../../../../node_modules/core-js/modules/es.typed-array.float64-array");
require("../../../../node_modules/core-js/modules/es.typed-array.int16-array");
require("../../../../node_modules/core-js/modules/es.typed-array.int32-array");
require("../../../../node_modules/core-js/modules/es.typed-array.int8-array");
require("../../../../node_modules/core-js/modules/es.typed-array.uint16-array");
require("../../../../node_modules/core-js/modules/es.typed-array.uint32-array");
require("../../../../node_modules/core-js/modules/es.typed-array.uint8-array");
require("../../../../node_modules/core-js/modules/es.typed-array.uint8-clamped-array");

AFAICT, typed-arrays are included either because 1) a bug in .toString in all versions of safari or 2) it is mistakenly not given a constraint for safari here

See the bottom of https://github.com/GoogleChrome/lighthouse/pull/10937#issuecomment-641744844 for why Promises are included.

Actions we can take:

  1. Do nothing, be ok with large polyfills in “modern” bundles
  2. Suggest excluding (via babel/preset-env exclude) type-arrays in the modern bundle, possibly also add a small polyfill to fix the toString issue (taking similar approach as babel/preset-modules and attempt to upstream to preset-env). Would be good to understand failure modes for this bug in older browsers.
  3. Suggest excluding Promise in the modern bundle. Again, maybe we can create a smaller polyfill to fix the thenable w/ error bug. (EDIT: actually this module would still get included, because other features like promise.finnaly, allSettled, etc pull in the promise module too …)

Related: https://github.com/GoogleChrome/web.dev/issues/3129 cc @housseindjirdeh Context: https://github.com/GoogleChrome/lighthouse/pull/10937#issuecomment-642320005

Issue Analytics

  • State:open
  • Created 3 years ago
  • Reactions:1
  • Comments:7 (1 by maintainers)

github_iconTop GitHub Comments

1reaction
patrickhulcecommented, Jun 11, 2020

possibly also add a small polyfill to fix the toString issue (taking similar approach as babel/preset-modules and attempt to upstream to preset-env)

I think this is an awesome idea. Even if it’s 10x the time/effort on our part, getting the default module/nomodule build path to not pull in a polyfill for all typedarray behavior will have 100x the impact. 👍

0reactions
paulirishcommented, Jun 23, 2020

For LH pov, we start with heavily recommending @babel/preset-env + esmodules: true + bugfixes: true.

Ideally we can resolve the promises/typedarrays polyfilling from within the babel-preset-env bugfixes path. An alternative is recommending some exclude patterns, but it’s not guaranteed to be totally fine.

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