in workbox-v4.3.1/workbox-window.dev.umd.js [406:427]
function Workbox(scriptURL, registerOptions) {
var _this;
if (registerOptions === void 0) {
registerOptions = {};
}
_this = _EventTargetShim.call(this) || this;
_this._scriptURL = scriptURL;
_this._registerOptions = registerOptions;
_this._updateFoundCount = 0; // Deferreds we can resolve later.
_this._swDeferred = new Deferred();
_this._activeDeferred = new Deferred();
_this._controllingDeferred = new Deferred(); // Bind event handler callbacks.
_this._onMessage = _this._onMessage.bind(_assertThisInitialized(_assertThisInitialized(_this)));
_this._onStateChange = _this._onStateChange.bind(_assertThisInitialized(_assertThisInitialized(_this)));
_this._onUpdateFound = _this._onUpdateFound.bind(_assertThisInitialized(_assertThisInitialized(_this)));
_this._onControllerChange = _this._onControllerChange.bind(_assertThisInitialized(_assertThisInitialized(_this)));
return _this;
}