To make sure your code can be easily maintained, you must first be sure to make it clean and tidy. This is the part where WebStorm really helps you. It automatically refactors your code by performing functions on it, such as extraction of variables, moving files, inline variable extraction, etc.

The local history feature in Webstorm tracks all your local changes in the source code that you are making. You can use it to view changes that you've made to your code and roll back whenever necessary.

WebStorm comes bundled with JSHint and JSLint. JSCS, ESLint, and 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 the user to view suggested fixes.

WebStorm has built-in support for CoffeeScript and Dart.

Webstorm supports not just Git and Mercurial, but Subversion, CVS, and Perforce as well.

WebStorm includes support for Meteor, Angular, and React.

The IDE comes with a built-in terminal, a feature lacking in some lighter editors.

WebStorm has a powerful debugger, with support for conditional breakpoints.

WebStorm (and really all of the IntelliJ IDEs) support the plugins throughout their plugin ecosystem which leaves you with 100s of tools to handle your automation tasks. There is a wide range of build-related plugins that help you by having pre-defined commands to execute with the click of a button. Out of any other IDE, WebStorm has by far the most coverage when it comes to tools for your development workflow.

WebStorm has built-in support for Sass which is one of the most stable and powerful CSS extension languages.

This integrates with other community tools like ESLint and editorconfig.

It is able to specify for example node versions, which will be used to run task for current project.

WebStorm offers typescript support for building typed JavaScript applications which improves refactoring and code completion, as well as helping to find bugs.

Makes adjusting an existing or creating new themes a breeze. Especially due to things like inheritance, as well as easily exporting/distributing/importing the color settings which really only store where on deviates from the defaults (thus the resulting files are very small and relatively human-readable).

Assists with configuration and understands module resolution.

Code Templates are powered by Apache VTL (Velocity Template Language) and allow for includes, custom variables, conditional blocks, iterators, and live templates.

WebStorm has a built-in webserver that allows you to run projects from http://localhost:63342/ProjectName.

WebStorm integrates with Node.js to allow for running, debugging, and unit testing of Node.js apps.

WebStorm has two types of autocompletion: structural completion and word expansion.

Structural autocompletion makes predictions based on its understanding of JavaScript objects, while the latter tries to predict the word currently being typed based on previously typed words. Word expansion also works in comments and docstrings and it's similar to vim's omnicompletion.

Both types of autocompletion work extremely well, have little to no problems and are quite fast even when loading suggestions on the go.