Wallaby.js is a continuous testing tool and IDE plugin for JavaScript and TypeScript. It automatically runs your tests as you write or edit code, displaying results, code coverage, and errors directly in your editor. Wallaby.js focuses on developer productivity by providing instant, actionable feedback and advanced debugging features, without requiring you to manually run test suites or leave your coding environment. It integrates with major editors and works with existing test frameworks, offering a seamless workflow for test-driven development and rapid iteration.

Key Features

Instant Test Feedback Provides real-time test results and code coverage as you type.

• Test results and coverage update instantly in the editor.
• No need to manually run tests or save files.

Time Travel Debugging Allows step-by-step navigation through code execution.

• Move forward and backward through code to inspect runtime states.
• Edit-and-continue support for rapid debugging cycles.

Smart Test Execution Runs only the minimum set of tests affected by code changes.

• Dependency analysis to detect impacted tests.
• Parallel execution for speed, even in large projects.

Inline Runtime Values and Error Reporting Displays variable values, errors, and logs next to code.

• Inline indicators for test failures and code errors.
• Direct feedback on code changes and test outcomes.

Code Coverage Visualization Shows real-time code coverage in the editor gutter.

• Highlights fully, partially, and uncovered lines.
• Helps identify untested or risky code areas.

Test and Coverage Explorer Offers a strategic overview of tests and coverage.

• Side-panel explorer for sorting, filtering, and navigating tests.
• Direct navigation to test sources and error lines.

Runtime Value Explorer Visualizes complex runtime values in a tree view.

• Explore object structures and copy values for inspection.
• Useful for debugging and understanding code behavior.

Enhanced Diffs & Snapshots Supports snapshot testing and diff visualization.

• Side-by-side diff views for expected vs. actual values.
• Editor commands for updating snapshots.

Benefits

Increased Developer Productivity Reduces feedback loop time and context switching.

• Instant feedback encourages frequent testing and code quality.
• Eliminates manual test runs and speeds up debugging.

Improved Code Quality Real-time coverage and error reporting help catch issues early.

• Inline feedback highlights problems as they are introduced.
• Supports test-driven development workflows.

Seamless Integration Works with existing editors and test frameworks.

• No vendor, API, or framework lock-in.
• Compatible with major JavaScript/TypeScript tools and IDEs.

Scalable for Large Projects Efficient test execution regardless of project size.

• Only affected tests run, minimizing wait times.
• Designed to maintain speed as codebases grow.