JavaScript Syntax Validator

Catch JavaScript syntax errors instantly using the browser’s own parser — code is compiled, never run.

Check JavaScript syntax instantly without running code. Free JS validator using the engine parser — syntax errors with line hints.

About JS Syntax Check

Catch JavaScript syntax errors instantly using the browser’s own parser — code is compiled, never run.

Paste code and choose script or module mode. The tool compiles it with the JavaScript engine’s own parser and reports the first syntax error with its message — or confirms validity. Nothing executes: no DOM, no network, no side effects possible.

Module mode strips import/export lines for the parse because the sync compiler only handles scripts; for full module fidelity use a bundler or tsc. This checks syntax only — logic, types, and runtime errors need real tooling.

Where it is used

Pre-flight checks before pasting snippets, validating minified output, teaching parser errors, and CI-adjacent quick checks.

How to use the JS Syntax Check

  1. JavaScript Code — enter the value (e.g. const x = 1; console.log(x);).
  2. Parse As — enter the value.
  3. Calculate — press the Calculate button to see the result instantly above.

Formula

Compile with the Function constructor (parse-only, never executed); report the first error.

Examples

Example

code:const x = 1; console.log(x;
mode:script
Result: Syntax error found (missing closing paren)

Frequently Asked Questions

Is my code executed?
No. The Function constructor parses (compiles) without running. Your code cannot access the page, network, or storage through this tool.
Why do import/export lines get special handling?
The synchronous parser only understands classic scripts. Module syntax is pre-stripped for the check, so module-only errors (like bad export names) may slip through.
Does valid syntax mean working code?
No — it means the grammar parses. Undefined variables, type errors, and logic bugs need linters, tests, and runtime checks.
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