chrome/renderer/resources/extensions/desktop_capture_custom_bindings.js

// Copyright 2013 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Custom binding for the desktopCapture API.

const idGenerator = requireNative('id_generator');

apiBridge.registerCustomHook(function(bindingsAPI) {
  const apiFunctions = bindingsAPI.apiFunctions;

  const pendingRequests = {};

  function onRequestResult(id, result, options) {
    if (id in pendingRequests) {
      const callback = pendingRequests[id];
      delete pendingRequests[id];
      callback(result, options);
    }
  }

  apiFunctions.setHandleRequest(
      'chooseDesktopMedia', function(sources, target_tab, options, callback) {
        // |target_tab| is an optional parameter.
        if (callback === undefined) {
          callback = target_tab;
          target_tab = undefined;
        }
        const id = idGenerator.GetNextId();
        pendingRequests[id] = callback;
        bindingUtil.sendRequest(
            'desktopCapture.chooseDesktopMedia',
            [
              id,
              sources,
              target_tab,
              options,
              $Function.bind(onRequestResult, null, id),
            ],
            undefined);
        return id;
      });

  apiFunctions.setHandleRequest('cancelChooseDesktopMedia', function(id) {
    if (id in pendingRequests) {
      delete pendingRequests[id];
      bindingUtil.sendRequest(
          'desktopCapture.cancelChooseDesktopMedia', [id], undefined,
          undefined);
    }
  });
});