JavaScript Validator

Paste JavaScript and see instantly whether the syntax is valid — error message, type, and line number shown in real time.

Last updated: May 29, 2026

JavaScript Code✓ Valid JavaScript

Lines: 7Characters: 163Functions: 1Classes: 0

Client-Side Processing

Input Data Stays on Device

Instant Local Execution

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What is JavaScript Validator?

JavaScript Validator checks JavaScript code for syntax errors using the browser's built-in JavaScript parser. It compiles the code to detect parse errors without executing it — the compiled function is immediately discarded. This means you get accurate syntax feedback (SyntaxError with message and location) without any code running. It validates as you type and shows a line count, character count, function count, and class count for valid code.

How to Use JavaScript Validator

Paste JavaScript code into the editor.

A Valid or Syntax Error badge updates as you type.

If there is an error, the message and line number are shown below.

Fix the error and the badge turns green.

Common Use Cases

Quickly checking a snippet for syntax errors before adding it to a project.
Verifying that generated or template-expanded JavaScript is well-formed.
Teaching JavaScript — immediately seeing where a mistake is in student code.
Sanity-checking code copied from documentation or Stack Overflow.

Example Input and Output

A function with a missing closing brace is detected as a syntax error.

JavaScript with error

function broken( {
  return 1;

Validation result

✗ Syntax Error
SyntaxError: Unexpected token '{'

Privacy

JavaScript code is validated locally in the browser and is never uploaded.

Frequently Asked Questions

Does this execute my code?

No. The validator uses new Function() to compile (parse) the code and immediately discards the result. No code is executed — only the parse step runs.

Does it catch all JavaScript errors?

It catches syntax errors (SyntaxError) that prevent code from parsing. It cannot detect runtime errors like ReferenceError or TypeError, which only appear when code actually runs. Use the JavaScript Tester tool to catch runtime errors.

Does it support TypeScript?

No. TypeScript includes type annotations that are not valid JavaScript syntax. Use a TypeScript compiler (tsc) to validate TypeScript.

Is my code uploaded anywhere?

No. Validation runs in your browser only.