CodeRunner 4 is a huge update with hundreds of new features and improvements, including:

• Error Checking and Linting. Get instant feedback on your code as you write it. CodeRunner checks your document for errors and common issues, underlining mistakes and describing the problem directly inline with your code. Compile and runtime issues in the console are automatically highlighted and included in the document. It's also easy to add support for third-party linters.
• Multiple Selections. CodeRunner 4's new editor supports fully context-independent multiple selections. Hold Command, Option, or Control-Shift while clicking or dragging to add multiple selections anywhere, allowing you to quickly make similar edits in multiple locations at once.
• Improved Highlighting with Code Tokenizers. Local variables, functions, and other code tokens are now highlighted on top of CodeRunner's powerful grammar-based syntax highlighting. In addition to providing better highlighting, this allows for quick and precise renaming of variables and other symbol names.
• Auto-Indent. All indentation functionality has been rewritten to be smarter and more deeply integrated into the editor. You can explicitly Auto-Indent an existing block of code using Control-I, but this is rarely needed since Auto-Indent is applied automatically as you type and when pasting code.
• Customizable Key Bindings. You can now customize the hundreds of existing keyboard shortcuts, and even add new shortcuts and macros directly in CodeRunner Preferences. A new Vim mode is also included.

Other notable features and improvements:

• New Find and Replace with support for regular expressions, multiple selections, and more.
• Improved code completion with extra-fuzzy search, completions beyond single words, and better documentation.
• Smart spell checking that ignores code and automatically checks segments of natural language.
• Improved debug console with syntax highlighting, code completion, and output filtering.
• Shell Script code completion for commands and their options, paths, and snippets, with built-in man-page lookups.
• Performance improvements delivering extremely fast syntax highlighting, code completion, and overall performance.
• Automatic closing of tags and other smart behaviors while typing.
• More customizable editor with a large number of new preferences and tweak-able behaviors.
• Select code structures by double-clicking edges of tag pairs, functions, if/else blocks, loops, etc.
• Node.js debugger, atomic spaces indentation, language groups, improved help, new keyboard shortcuts, and more.