Learning by Hacking

Why a re-introduction? Because JavaScript has a reasonable claim to being the world's most misunderstood programming language. While often derided as a toy, beneath its deceptive simplicity lie some powerful language features. 2005 saw the launch of a number of high-profile JavaScript applications, showing that deeper knowledge of this technology is an important skill for any web developer.

This was inspired by, and based on @lensco's excellent Simple Responsive Design Test Page. It lets you view any webpage in multiple screen sizes, simulating the viewport of different devices. After getting such a positive response to my original post, I thought I'd expand on it a little. Since people are obviously targeting different device screen sizes with their projects, the form below now lets you generate a custom bookmarklet that displays only those device sizes you're interested in.