javascript - dynamically created iframe triggers onload event twice

Question

I created an iframe dynamically and found that this iframe trigger onload event twice.

var i=0;
frameOnload=function(){
  console.log(i++);  
};

var ifr=document.createElement("iframe");  
ifr.src="javascript:(function(){document.open();document.write('test');document.close();})();";
ifr.onload=frameOnload;  
document.body.appendChild(ifr);

Why i finally is 1?
How to prevent iframe's onload twice instead of pointing onload function to null inside itself?

Answer 1

I've also encountered the same problem, but get no answer anywhere, so I tested by myself.

The iframe onload event will be triggered twice in webkit browsers ( safari/chrome ), if you attach the onload event BEFORE the iframe is appended to the body.

So you can prevent iframe onload twice by change your codes in the following way.

document.body.appendChild(ifr);
ifr.onload=frameOnload; // attach onload event after the iframe is added to the body

Then, you will only get one onload event, which is the event the document really loaded.