Validate JavaScript online. Check for syntax errors, loose equality, leftover console/debugger statements, eval(), and other common bugs. Free, instant, runs in your browser.
JavaScript validation checks your code for syntax errors, problematic patterns, and common bugs. Catching these issues before running code in a browser saves debugging time and prevents silent failures that only surface at runtime.
This validator checks for: syntax errors (using the browser's own parser), loose equality (==), var usage, console.log and debugger statements left in, eval() calls, document.write(), and potential XSS via innerHTML. It does not perform TypeScript type checking or full ESLint-level analysis.
JavaScript's == operator performs type coercion before comparing, which causes surprising results: 0 == false is true, "" == 0 is true. The strict operator === compares both value and type without coercion, making comparisons predictable and bugs less likely.
No. Syntax checking uses the browser's built-in new Function() parser, and static analysis is done entirely in JavaScript. Your code never leaves your machine.
For production projects, use ESLint with a configuration file checked into your repository. ESLint supports hundreds of rules, TypeScript, JSX, custom plugins, and IDE integration. This tool is best for quick one-off checks of standalone scripts or learning why a pattern is considered problematic.