feat(elements): add support for creating custom elements (#22413)

PR Close #22413

packages/elements/src/utils.ts

@@ -0,0 +1,103 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {Type} from '@angular/core';
+
+const elProto = Element.prototype as any;
+const matches = elProto.matches || elProto.matchesSelector || elProto.mozMatchesSelector ||
+    elProto.msMatchesSelector || elProto.oMatchesSelector || elProto.webkitMatchesSelector;
+
+/**
+ * Provide methods for scheduling the execution of a callback.
+ */
+export const scheduler = {
+  /**
+   * Schedule a callback to be called after some delay.
+   *
+   * Returns a function that when executed will cancel the scheduled function.
+   */
+  schedule(taskFn: () => void, delay: number): () =>
+      void{const id = window.setTimeout(taskFn, delay); return () => window.clearTimeout(id);},
+
+  /**
+   * Schedule a callback to be called before the next render.
+   * (If `window.requestAnimationFrame()` is not available, use `scheduler.schedule()` instead.)
+   *
+   * Returns a function that when executed will cancel the scheduled function.
+   */
+  scheduleBeforeRender(taskFn: () => void): () => void{
+    // TODO(gkalpak): Implement a better way of accessing `requestAnimationFrame()`
+    //                (e.g. accounting for vendor prefix, SSR-compatibility, etc).
+    if (typeof window.requestAnimationFrame === 'undefined') {
+      const frameMs = 16;
+      return scheduler.schedule(taskFn, frameMs);
+    }
+
+    const id = window.requestAnimationFrame(taskFn);
+    return () => window.cancelAnimationFrame(id);
+  },
+};
+
+/**
+ * Convert a camelCased string to kebab-cased.
+ */
+export function camelToKebabCase(input: string): string {
+  return input.replace(/[A-Z]/g, char => `-${char.toLowerCase()}`);
+}
+
+/**
+ * Create a `CustomEvent` (even on browsers where `CustomEvent` is not a constructor).
+ */
+export function createCustomEvent(doc: Document, name: string, detail: any): CustomEvent {
+  const bubbles = false;
+  const cancelable = false;
+
+  // On IE9-11, `CustomEvent` is not a constructor.
+  if (typeof CustomEvent !== 'function') {
+    const event = doc.createEvent('CustomEvent');
+    event.initCustomEvent(name, bubbles, cancelable, detail);
+    return event;
+  }
+
+  return new CustomEvent(name, {bubbles, cancelable, detail});
+}
+
+/**
+ * Check whether the input is an `Element`.
+ */
+export function isElement(node: Node): node is Element {
+  return node.nodeType === Node.ELEMENT_NODE;
+}
+
+/**
+ * Check whether the input is a function.
+ */
+export function isFunction(value: any): value is Function {
+  return typeof value === 'function';
+}
+
+/**
+ * Convert a kebab-cased string to camelCased.
+ */
+export function kebabToCamelCase(input: string): string {
+  return input.replace(/-([a-z\d])/g, (_, char) => char.toUpperCase());
+}
+
+/**
+ * Check whether an `Element` matches a CSS selector.
+ */
+export function matchesSelector(element: Element, selector: string): boolean {
+  return matches.call(element, selector);
+}
+
+/**
+ * Test two values for strict equality, accounting for the fact that `NaN !== NaN`.
+ */
+export function strictEquals(value1: any, value2: any): boolean {
+  return value1 === value2 || (value1 !== value1 && value2 !== value2);
+}