client/lib/popup-monitor/index.js
function PopupMonitor() {
	this.intervals = {};
	this.monitorInterval = null;
	this.windowInstance = null;
	this.onMessage = messageEvent => {
		if ( messageEvent.source === this.windowInstance ) {
			this.emit( 'message', messageEvent.data );
		}
	};
}
function PopupMonitor() {
	this.intervals = {};
	this.monitorInterval = null;
	this.windowInstance = null;
	this.onMessage = messageEvent => {
		if ( messageEvent.source === this.windowInstance ) {
			this.emit( 'message', messageEvent.data );
		}
	};
}
PopupMonitor component

@public