JavaScript tools

Editors and IDEs

1. Scintilla and SciTE: text editor
2. Notepad++: text editor (based on Scintilla)
3. Komodo Edit: text editor
4. Aptana Studio: IDE (based on Eclipse)
5. WebStorm IDE: commercial IDE

Firefox

1. Built-in error console: Ctrl-Shift-J
2. Firefox extensions are available at addons.mozilla.org
3. Web Developer: many tools for inspecting and validating a web page
4. Firebug: inspect, edit, and debug HTML, CSS, and JavaScript on current page
5. Greasemonkey: lets you modify a page when it loads using JavaScript
6. Console²: advanced JavaScript console

Chrome

1. Built-in developer tools: Ctrl-Shift-I, or hotdog-menu -> Tools -> Developer Tools
2. Chrome extensions are available in the Chrome web store
3. Web Developer: many tools for inspecting and validating a web page
4. Pendule: additional tools for inspecting a web page
5. Validity: HTML validator

Opera

1. Built-in developer tools (Dragonfly): Ctrl-Shift-I

Safari

1. Built-in developer tools (Advanced preferences -> Show Develop menu in menu bar

Internet Explorer

1. Built-in developer tool: F12

JavaScript testing online

1. JS Bin: Interactive online JavaScript tester
2. JSFiddle: Interactive online JavaScript tester
3. JSLint: JavaScript code quality tool
4. JSHint: JavaScript code quality tool

JavaScript minifiers and obfuscator

1. Google's Closure compiler: JavaScript minifier
2. YUI Compressor: Yahoo's JavaScript and CSS minifier
3. Daft Logic online JavaScript obfuscator