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Pro Code refactoring support
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.
Pro Intelligent code completion
Webstorm will auto complete JS variables, keywords, methods, functions, and parameters. Webstorm can also offer completion from methods and functions that are in any external libraries or frameworks.
Pro Node.js integration
WebStorm integrates with Node.js to allow for running, debugging, and unit testing of Node.js apps.
Pro Integrated code quality tools
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 includes support for Meteor, Angular, and React.
Pro Maintains a local history
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.
Pro Powerful git and GitHub integration
WebStorm has a powerful visual git tool, allowing for easy commits, visual diffing, merging, push/pull, rebasing, and inspecting the VCS history of a project. GitHub is supported natively - you can check out a project directly from GitHub.
Pro Supports a wide range of plug-ins
Pro Typescript support
Pro Built-in web server
WebStorm has a built-in webserver that allows you to run projects from
Pro Built-in terminal/run tools
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 support for Grunt and Gulp task runners.
WebStorm has built-in support for CoffeeScript and Dart.
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 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.
Pro CSS pre-processor support
WebStorm has built-in support for Sass which is one of the most stable and powerful CSS extension languages.
Pro Server and client-side debugger
WebStorm has a powerful debugger, with support for conditional breakpoints.
Pro Support for Karma test runner
Pro Theme support / tweaking
The theme is very easy to customize to your liking. You can change font-size, colors, highlighting colors, and more.
Pro Support for all major VCS systems
Webstorm supports not just Git and Mercurial, but Subversion, CVS, and Perforce as well.
Pro Multi-line select and editing
Pro Efficient and effective
Pro Really good configurable code formatting
Pro Free for open-source development, students, and teacher
Non-commercial open source projects, and students and teachers (including classroom licenses) may qualify for a free license. There is a 50% off license for startups (under 3 years old). You can read more about it here.
Pro Special icons for most filetypes in project list
Webstorm comes with icons for many filetypes which makes it easier to find what you're looking for in the project list.
Pro Powerful Code Templates
Code Templates are powered by Apache VTL (Velocity Template Language) and allow for includes, custom variables, conditional blocks, iterators, and live templates.
Pro Cordova support
Pro Includes terminal
The IDE comes with a built-in terminal, a feature lacking in some lighter editors.
Pro Auto sync settings across team / machines / platforms
With the Settings Repository, you can easily enforce your development standards.
Pro Dartlang support
Autocompletion, syntax-highlighting, refactoring, and pub integration for Dart are supported in WebStorm.
Pro Coffeescript support
Con Occasional slow performance
Con Non-native filesystem causes issues
The Java wrapper around the filesystem doesn't actively watch for file changes (by, for example, using the fsevents api on OS X), and as a result can become easily desynchronised from the actual filesystem.
It should be noted though that this is easily remedied by going to File/Settings/System Settings and checking the "Synchronize Files on frame or editor tab activation" option. It's also recommended to more explicitly represent your workflow within WebStorm itself. Most external tools/tasks can be handled with WebStorm. And if it's not in a plug-in, then you can handle it with the File Watchers.
Con Poor usability on option and menu navigation
You need to press a combination of keys or navigate through different menu levels to carry out the two most common things a developer does. For example, to run your code, the default is Shift+F10. To go to definition, you need to click on "Navigation" first. There is no sense to this: being forced to press a combination of keys hundreds of times or navigating through different menus can be a waste of time.
Con Not free for commercial use
A paid license is required to use WebStorm for commercial use. The license terms changed in November 2015 and currently require a subscription (per year: $59 personal, $129 for companies). Students can obtain a free non-commercial, educational license good for one year. There is also an option to pay on a monthly basis in addition to perks, such as a fallback commercial license that can be used for free.
Con You have to fiddle with the JVM memory settings in configuration files
To get it to run properly, you have to edit the JVM memory settings when you use Node.js. Node.js makes the small JS project you have into a "large" project that requires more memory.
Con Not open source
This application is proprietary, and thus cannot be modified, freely distributed, or trusted for security.
Con Proprietary file dialogs
Webstorm doesn't use the native Windows and OSX file dialogs, which makes it more of a hassle to open projects.
For instance, you don't have access to your favorite folders on the left-hand side in their custom file dialogs.
Con Can't open multiple projects in a single instance
The only way to open multiple projects is to run a new instance of WebStorm which is not ideal. WebStorm can use up to 1-1.5 GB of memory.
Con Newer versions are increasingly unstable
Con Constantly trailing behind on support for its main features
The Jetbrains team do an admirable job attempting to keep up with support for the features they wrap, but they are running an un-winnable race. For example, WebStorm 11.0.2 hangs when trying to debug NodeJS 5.0+ projects (30+ seconds before hitting breakpoint). By the time they fix it, 5.1 will be out and something else will break.