Question 1

How does this check syntax without running my code?

Accepted Answer

It passes your code to the JavaScript `Function` constructor, which parses the code into a callable function object but does not invoke it. Parsing happens the same way it would for any script — using the browser's real JS engine — so a genuine syntax error throws a real SyntaxError, but your code's logic never actually runs.

Question 2

Is it safe to paste code I don't fully trust?

Accepted Answer

Syntax checking alone is safe since the code is only parsed, not executed — but this tool has no 'run' button and never calls the resulting function, so even code with side effects if executed won't do anything here.

Question 3

Why doesn't it always show an exact line number?

Accepted Answer

Line/column reporting for syntax errors from `Function()` isn't consistently exposed across browsers — some engines attach a `lineNumber` property, others don't. When available, it's shown as an approximate location; when not, you still get the full error message, which is usually enough to locate the issue.

Question 4

Does this check TypeScript syntax too?

Accepted Answer

No — this checks plain JavaScript only. TypeScript-specific syntax (type annotations, interfaces, generics) will report as a syntax error since it isn't valid JavaScript on its own.

Question 5

Can it check ES modules with import/export statements?

Accepted Answer

No — `Function()`-based parsing only supports script-level syntax, not module syntax. Paste the code body without top-level import/export statements to check it.

Question 6

Is my code sent anywhere?

Accepted Answer

No, all parsing happens locally in your browser — no upload.

JavaScript Syntax Checker

JavaScript Syntax Checker: Real Parsing, Not a Guess