Iframe creating multiple events for document open in Ionic4

I have created a iframe for loading billing pages, in ngAfterViewInit() appending src url to it. After page load for opening PDF documents added window.addEventListener in onLoad() method of iframe. It is creating multiple events while opening and closing PDF docs which is creating redundent document opens. It is happening only for ionic V4 version. Any one facing similar issue? Please help.

@ViewChild(‘iframe’, { static: false }) iframe: ElementRef;
check if iframe is present or not
if (this.iframe) {
//logic goes here