How to listen for child window closing?

If you store a reference to the child window when you call window.open(), then you can poll using setInterval() to see whether the window is still open using the window.closed property. The example below checks twice per second.

var child = window.open('http://google.com','','toolbar=0,status=0,width=626,height=436');
var timer = setInterval(checkChild, 500);

function checkChild() {
    if (child.closed) {
        alert("Child window closed");   
        clearInterval(timer);
    }
}

Note to others: If you are ever in a situation where you have control over the html in the child window, you could make use of the onbeforeunload event and alert the parent window.

For future references, I'd like to share another solution that doesn't require setInterval :

var child = window.open('http://google.com','','toolbar=0,status=0,width=626,height=436');
child.onunload = function(){ console.log('Child window closed'); };