IFRAME contentWindow is null
I like clean code so I do what I can to avoid unwanted JavaScript global variables. I initially thought that keys(window) would give me window property leaks but that didn't work because browsers returned different results, so I moved on to using an IFRAME to compare default window property keys.
When I first tried this method, I got a lame error about an IFRAME element's contentWindow property being null. Ugh. It didn't take long to figure out why: you need to wait until the IFRAME has loaded to get the contentWindow:
var iframe = document.createElement('iframe');
iframe.onload = function() {
// contentWindow is set!
};
iframe.src = 'about:blank';
document.body.appendChild(iframe);
Of course you'll want to add the onload event before setting the src. If you use the load event to check for the contentWindow property, you'll be in business!
![39 Shirts – Leaving Mozilla]()
In 2001 I had just graduated from a small town high school and headed off to a small town college. I found myself in the quaint computer lab where the substandard computers featured two browsers: Internet Explorer and Mozilla. It was this lab where I fell...
![Write Better JavaScript with Promises]()
You've probably heard the talk around the water cooler about how promises are the future. All of the cool kids are using them, but you don't see what makes them so special. Can't you just use a callback? What's the big deal? In this article, we'll...
![Select Dropdowns, MooTools, and CSS Print]()
I know I've harped on this over and over again but it's important to enhance pages for print. You can do some things using simple CSS but today's post features MooTools and jQuery. We'll be taking the options of a SELECT element and generating...
![MooTools-Like Element Creation in jQuery]()
I really dislike jQuery's element creation syntax. It's basically the same as typing out HTML but within a JavaScript string...ugly! Luckily Basil Goldman has created a jQuery plugin that allows you to create elements using MooTools-like syntax.
Standard jQuery Element Creation
Looks exactly like writing out...
Don’t you need to append your iframe element to a DOM tree so that the browser fetches its target content ? I mean, I know that old IE will load scripts as you parse an “HTML string” but in modern browsers, I thought that the asset does not get loaded until you append the element to a document (and in my opinion this it what makes constructors such as
Image()so useful).Yes, good catch! Updated!
Unfortunately this does not appear to be 100% reliable in chrome (i’m currently using version 62.0.3202.94, but this appears to have been an issue for a while), as sometimes contentWindow can still be null when onload is triggered.
This solution worked for me! Thanks a lot!
Thank you, saved me hours!
Sharry