JavaScript Validator: Check Syntax and Find Errors
JavaScript Validator parses JavaScript with Acorn to identify syntax errors and show their exact line and column, along with a code frame. Select an ECMAScript version and choose module or script mode to match your code. You can also use lightweight lint warnings for issues such as unused variables and loose equality; warnings are clearly distinguished from syntax errors.
JavaScript Validator is a browser-based JavaScript syntax checker for developers who want clear feedback while reviewing code. Use this JavaScript Validator to parse code with Acorn, find syntax errors, and see where they occur without having to scan the whole file manually. It also offers optional lightweight lint warnings for selected code issues.
The validator lets you choose an ECMAScript version and whether to parse the input as a module or a script. When the parser finds a syntax error, it reports the exact line and column and provides a code frame to help you locate it. Optional warnings can flag unused variables, loose equality (== vs ===), and more; they are labeled as warnings, not errors.
Syntax validation and lint feedback serve different purposes: a syntax error means the code could not be parsed under the selected settings, while a lint warning points out a potential issue without labeling it as a syntax error. JavaScript's module and script modes provide different parsing contexts, so selecting the appropriate mode helps you check code as intended. The ECMAScript version setting lets you choose the version used for parsing.
JavaScript Validator runs entirely in your browser. Your input is processed on your own device and nothing is uploaded, stored, or sent to a server. Once the page has loaded, the tool works offline, so you can validate code without an ongoing internet connection.
The tool is useful for developers and DevOps engineers checking handwritten JavaScript, reviewing code from another tool, or pinpointing a parser error before a later workflow step. Beginners can use the line, column, and code frame to find syntax problems, while experienced developers can quickly check version and module or script settings and review optional lint warnings.
Step 1: Paste or drop your JavaScript into the validator. Use the code you want to check, including output generated by another tool.
Step 2: Choose an ECMAScript version and select module or script mode. Matching these settings to your code helps the parser check it in the intended context.
Step 3: Run the check to parse your JavaScript with Acorn. The validator reports syntax errors when it finds them.
Step 4: Review any error's line and column position and the accompanying code frame to locate the problem.
Step 5: If you want additional feedback, use the optional lightweight lint warnings to check for issues such as unused variables or loose equality.
Use case: Check a JavaScript file before it reaches a parser or runtime step, so you can catch syntax errors earlier.
Use case: Find the exact line and column of a syntax error instead of searching through the file by hand.
Use case: Verify that code produced by another tool is valid JavaScript, not just plausible-looking output.
Use case: Check code using the ECMAScript version you need, helping you spot syntax that does not parse under that selection.
Use case: Choose module or script mode to check JavaScript in the context that matches how the code is intended to be parsed.
Use case: Review optional warnings for unused variables and loose equality as an extra check beyond syntax validation.