Class PlatformBrowser

tfjs-core/src/platforms/platform_browser.ts:28–99

import {isTypedArrayBrowser} from './is_typed_array_browser';

export class PlatformBrowser implements Platform {
  // According to the spec, the built-in encoder can do only UTF-8 encoding.
  // https://developer.mozilla.org/en-US/docs/Web/API/TextEncoder/TextEncoder
  private textEncoder: TextEncoder;

  // For setTimeoutCustom
  private readonly messageName = 'setTimeoutCustom';
  private functionRefs: Function[] = [];
  private handledMessageCount = 0;
  private hasEventListener = false;

  fetch(path: string, init?: RequestInit): Promise<Response> {
    return fetch(path, init);
  }

  now(): number {
    return performance.now();
  }

  encode(text: string, encoding: string): Uint8Array {
    if (encoding !== 'utf-8' && encoding !== 'utf8') {
      throw new Error(
          `Browser's encoder only supports utf-8, but got ${encoding}`);
    }
    if (this.textEncoder == null) {
      this.textEncoder = new TextEncoder();
    }
    return this.textEncoder.encode(text);
  }
  decode(bytes: Uint8Array, encoding: string): string {
    return new TextDecoder(encoding).decode(bytes);
  }

  // If the setTimeout nesting level is greater than 5 and timeout is less
  // than 4ms, timeout will be clamped to 4ms, which hurts the perf.
  // Interleaving window.postMessage and setTimeout will trick the browser and
  // avoid the clamp.
  setTimeoutCustom(functionRef: Function, delay: number): void {
    if (typeof window === 'undefined' ||
        !env().getBool('USE_SETTIMEOUTCUSTOM')) {
      setTimeout(functionRef, delay);
      return;
    }

    this.functionRefs.push(functionRef);
    setTimeout(() => {
      window.postMessage(
          {name: this.messageName, index: this.functionRefs.length - 1}, '*');
    }, delay);

    if (!this.hasEventListener) {
      this.hasEventListener = true;
      window.addEventListener('message', (event: MessageEvent) => {
        if (event.source === window && event.data.name === this.messageName) {
          event.stopPropagation();
          const functionRef = this.functionRefs[event.data.index];
          functionRef();
          this.handledMessageCount++;