I first got hip to the guys at a JetBrains a few years back while trying to find a nasty memory leak in a Windows app. I was using a free tool from Microsoft that was not helping me find the issue. I was contemplating writing my own tool, when a fellow team member suggested using dotTrace since we had a corporate license. Once I got comfortable with the tool, I was quickly able to find out that we had not one but several memory leaks. I resolved them all in less than two days.
My next encounter with JetBrains was winning a years license for ReSharper about a year ago. The license sat unused until most of the year had elapsed. Finally one Saturday morning I installed it. I was thoroughly impressed. It was actually able to improve Visual Studio already excellent intellisense feature. And it was able to help me write better code by making suggestion to my code while I was writing it. Possibly the most impressive thing of all this was that it didn't make my dev box feel sluggish. I had tried another IDE enhancer and it made my machine noticeably slower and I quickly uninstalled it.
What's so great about? There are three main things I like about WebStorm: it helps you to write code quicker, it helps reduce your mistakes, and it helps increase the quality of your code.
Write Code Quicker
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Reduce Your Mistakes
Increase the Quality of Your Code
WebStorm removes all of the friction. Assuming that you have written some test cases in JsTestDriver's format, all you have to do is hover above a "TestCase" right click and choose, "Add JsTestDriver assertion framework support". The supporting structure for the framework will be added to your project. Then click the "JsTestDriver" tab at the bottom of the IDE to see its control panel. Clicking the green arrow, will spin up JsTestDriver's server. Clicking on any of the browser icons will launch the browser and point it to JsTestDriver's server. After starting all of your browsers you only need to click the green go arrow to execute your tests against each browser. You can even execute test with coverage so you have some idea of how much of your code has unit tests and how much is naked.
This is an unbelievably good development tool, but it isn't perfect. Sometimes the tool tips won't go away automatically. Pressing the escape key once or twice will make it disappear. Also the documentation and tutorials are a bit disjointed. WebStorm and its sister PHPStorm are both based on JetBrains' IntelliJ platform, so especially in videos, they may be using one of those other products, and as a result what you see on the screen may not exactly match what you see on your machine.
JetBrains' WebStorm 4.0