Recs.
Updated
SpecsUpdate
Pros
Pro Code refactoring support
To make sure your code can be easily maintained, you must first be sure to make it is clean and tidy. This is the part where WebStorm really helps you, it automatically refactors your code by performing on it functions such as extraction of variables, moving files, inline variable extraction etc..
Pro Ability to base hot keys on previously used IDEs
When you install WebStorm, it allows you to choose from other IDE's for it to base it's hot keys on. So if you are switching from another IDE, it makes it a very easy transition and productivity is not adversely affected by having to learn new hot keys.
Pro Integrated code quality tools
WebStorm comes bundled with JSHint, JSLint JavaScript linters. JSCS, ESLint as well as Closure Linter can be installed via npm. They register as inspections and are customizable through IDE settings. They run automatically and will highlight potential issues. Pressing alt+enter on an issue will allow viewing suggested fixes.
Pro Reduces the amount of repetitive code that has to be written with code snippets
WebStorm includes a feature called Live Templates. Live Templates are predefined code snippets that can include variables. They're intended to increase productivity by reducing the amount of repetitive code that has to be written.
Cons
Con Not free for commercial use
A paid license is required to use WebStorm for commercial use. The license terms have changed (Nov 2015) and now require a subscription (per year: $59 personal, $129 for companies). Students can obtain a free non-commercial, educational license good for 1 year.