♻️ Modernize polyfills

src/polyfills/custom-elements.js

@@ -15,6 +15,8 @@
  */
 
 import {Deferred} from '../core/data-structures/promise';
+import {map} from '../core/types/object';
+import {rethrowAsync} from '../core/error';
 
 /**
  * For type anotations where Element is a local variable.
@@ -98,19 +100,6 @@ function isPatched(win) {
  return tag.indexOf('[native code]') === -1;
 }
 
-/**
- * Throws the error outside the current event loop.
- * TODO(rcebulko): Condense with core/error#rethrowAsync
- *
- * @param {!Error} error
- */
-function rethrowAsync(error) {
- setTimeout(() => {
- self.__AMP_REPORT_ERROR(error);
- throw error;
- });
-}
-
 /**
  * The public Custom Elements API.
  */
@@ -127,7 +116,7 @@ class CustomElementRegistry {
  this.registry_ = registry;
 
  /** @private @const @type {!Object<string, !Deferred>} */
- this.pendingDefines_ = Object.create(null);
+ this.pendingDefines_ = map();
  }
 
  /**
@@ -212,7 +201,7 @@ class Registry {
  this.win_ = win;
 
  /** @private @const @type {!Object<string, !CustomElementDef>} */
- this.definitions_ = Object.create(null);
+ this.definitions_ = map();
 
  /**
  * A up-to-date DOM selector for all custom elements.
@@ -320,9 +309,9 @@ class Registry {
  };
 
  this.observe_(name);
- this.roots_.forEach((tree) => {
+ for (const tree of this.roots_) {
  this.upgrade(tree, name);
- });
+ }
  }
 
  /**
@@ -342,8 +331,7 @@ class Registry {
  const query = opt_query || this.query_;
  const upgradeCandidates = this.queryAll_(root, query);
 
- for (let i = 0; i < upgradeCandidates.length; i++) {
- const candidate = upgradeCandidates[i];
+ for (const candidate of upgradeCandidates) {
  if (newlyDefined) {
  this.connectedCallback_(candidate);
  } else {
@@ -491,9 +479,9 @@ class Registry {
  // I would love to not have to hold onto all of the roots, since it's a
  // memory leak. Unfortunately, there's no way to iterate a list and hold
  // onto its contents weakly.
- this.roots_.forEach((tree) => {
+ for (const tree of this.roots_) {
  mo.observe(tree, TRACK_SUBTREE);
- });
+ }
 
  installPatches(this.win_, this);
  }
@@ -530,28 +518,25 @@ class Registry {
  * @param {!Array<!MutationRecord>} records
  */
  handleRecords_(records) {
- for (let i = 0; i < records.length; i++) {
- const record = records[i];
+ for (const record of records) {
  if (!record) {
  continue;
  }
 
  const {addedNodes, removedNodes} = record;
- for (let i = 0; i < addedNodes.length; i++) {
- const node = addedNodes[i];
+ for (const node of addedNodes) {
  const connectedCandidates = this.queryAll_(node, this.query_);
  this.connectedCallback_(node);
- for (let i = 0; i < connectedCandidates.length; i++) {
- this.connectedCallback_(connectedCandidates[i]);
+ for (const candidate of connectedCandidates) {
+ this.connectedCallback_(candidate);
  }
  }
 
- for (let i = 0; i < removedNodes.length; i++) {
- const node = removedNodes[i];
+ for (const node of removedNodes) {
  const disconnectedCandidates = this.queryAll_(node, this.query_);
  this.disconnectedCallback_(node);
- for (let i = 0; i < disconnectedCandidates.length; i++) {
- this.disconnectedCallback_(disconnectedCandidates[i]);
+ for (const candidate of disconnectedCandidates) {
+ this.disconnectedCallback_(candidates);
  }
  }
  }
@@ -660,7 +645,7 @@ function installPatches(win, registry) {
  'innerHTML'
  );
  }
- if (innerHTMLDesc && innerHTMLDesc.configurable) {
+ if (innerHTMLDesc?.configurable) {
  const innerHTMLSetter = innerHTMLDesc.set;
  innerHTMLDesc.set = function (html) {
  innerHTMLSetter.call(this, html);
@@ -884,9 +869,7 @@ export function copyProperties(obj, prototype) {
  break;
  }
 
- const props = Object.getOwnPropertyNames(current);
- for (let i = 0; i < props.length; i++) {
- const prop = props[i];
+ for (const prop of Object.getOwnPropertyNames(current)) {
  if (Object.hasOwnProperty.call(obj, prop)) {
  continue;
  }
@@ -949,7 +932,7 @@ export function install(win, ctor) {
 
  // If that didn't throw, we're transpiled.
  // Let's find out if we can wrap HTMLElement and avoid a full patch.
- installWrapper = !!(Reflect && Reflect.construct);
+ installWrapper = !!Reflect?.construct;
  } catch (e) {
  // The ctor threw when we constructed it via ES5, so it's a real class.
  // We're ok to not install the polyfill.

src/polyfills/fetch.js

@@ -55,7 +55,7 @@ let XMLHttpRequestDef;
  * @return {!Promise<!FetchResponse>}
  */
 export function fetchPolyfill(input, init = {}) {
- return new Promise(function (resolve, reject) {
+ return new Promise((resolve, reject) => {
  const requestMethod = normalizeMethod(init.method || 'GET');
  const xhr = createXhrRequest(requestMethod, input);
 
@@ -68,9 +68,9 @@ export function fetchPolyfill(input, init = {}) {
  }
 
  if (init.headers) {
- Object.keys(init.headers).forEach(function (header) {
+ for (const header of Object.keys(init.headers)) {
  xhr.setRequestHeader(header, init.headers[header]);
- });
+ }
  }
 
  xhr.onreadystatechange = () => {
@@ -280,12 +280,12 @@ export class Response extends FetchResponse {
  data.status = init.status === undefined ? 200 : parseInt(init.status, 10);
 
  if (isArray(init.headers)) {
- /** @type {!Array} */ (init.headers).forEach((entry) => {
+ for (const entry of /** @type {!Array} */ (init.headers)) {
  const headerName = entry[0];
  const headerValue = entry[1];
  lowercasedHeaders[String(headerName).toLowerCase()] =
  String(headerValue);
- });
+ }
  } else if (isObject(init.headers)) {
  for (const key in init.headers) {
  lowercasedHeaders[String(key).toLowerCase()] = String(

src/polyfills/object-assign.js

@@ -30,8 +30,7 @@ export function assign(target, var_args) {
  }
 
  const output = Object(target);
- for (let i = 1; i < arguments.length; i++) {
- const source = arguments[i];
+ for (const source of arguments) {
  if (source != null) {
  for (const key in source) {
  if (hasOwnProperty.call(source, key)) {

src/polyfills/stubs/intersection-observer-stub.js

@@ -268,7 +268,9 @@ export class IntersectionObserverStub {
  upgrade_(Ctor) {
  const inst = new Ctor(this.callback_, this.options_);
  this.inst_ = inst;
- this.elements_.forEach((e) => inst.observe(e));
+ for (const e of this.elements_) {
+ inst.observe(e);
+ }
  this.elements_ = null;
  }
 }

src/polyfills/stubs/resize-observer-stub.js

@@ -72,7 +72,9 @@ export function upgradePolyfill(win, installer) {
  const upgrade = (upgrader) => {
  microtask.then(() => upgrader(Polyfill));
  };
- upgraders.forEach(upgrade);
+ for (const upgrader of upgraders) {
+ upgrade(upgrader);
+ }
  Stub[UPGRADERS] = {'push': upgrade};
  } else {
  // Even if this is not the stub, we still may need to install the polyfill.
@@ -144,7 +146,9 @@ export class ResizeObserverStub {
  upgrade_(Ctor) {
  const inst = new Ctor(this.callback_);
  this.inst_ = inst;
- this.elements_.forEach((e) => inst.observe(e));
+ for (const e of this.elements_) {
+ inst.observe(e);
+ }
  this.elements_ = null;
  }
 }