Suitable window.showModalDialog replacement when we have to pause execution of Parent page till Child process is done

Question

I want to replace window.showModalDialog in existing code in order to make it run in edge.

In this on a button click User will be presented with a custom attachment page (Child page). when he will fill out the details and attach a file. once he attach and click on save i want the control to be back on Parent page and continue the execution.

I tried using Event listener but was not able to Pause the execution.

//Start of execution

document.getElementById("button").click();
var retVal = window.showModalDialog(url, "", WinSettings);
//stop the execution till user save the file
if (retVal == 1) {
//Some process
return true;

//Continue execution