⚡

JavaScript Validator & Syntax Checker ⚡ ES2022 Valid

Validate JavaScript source code, detect syntax errors, unclosed braces, accidental assignments, and verify ES6+ compliance with an instant quality score.

More Free Tools:

🎨 CSS Validator 🔍 HTML Validator 🌐 HTML Formatter {} JSON Formatter ⇄ Text Diff Checker Aa Case Converter 📝 Word Counter 64 Base64 Encoder 💡 Suggest a Tool

Why Validate Your JavaScript?

Even experienced developers make simple typos like forgetting a closing curly bracket, missing a comma, or writing a single = instead of ===. Because JavaScript runs directly in your visitor's browser, a single syntax mistake can freeze your webpage, break a checkout form, or stop buttons from working.

This free tool catches those bugs instantly before you publish changes. It inspects your code right inside your browser, explains any issues in plain English, and lets you click directly to the problem line so you can fix it in seconds.

How to Check & Fix Your Code in 3 Simple Steps

Paste or Upload Your Code: Paste your JavaScript into the left editor, or click Upload File to inspect any .js, .mjs, or .txt file directly from your computer.
Click Any Error to Jump to That Line: Look at the report on the right. If any issues are found, click on any issue card to jump straight to that line in your code and view the suggested fix.
Format & Clean: Click Format JS to clean up messy indentation and brackets, then copy your clean code right back into your project.

Common JavaScript Bugs Explained in Plain English

Here is a breakdown of the common issues our tool checks for and why fixing them matters for your site:

Common Bug	Severity	What Happens If You Don't Fix It	How to Fix It
Missing bracket '}', ')', or ']'	Error	Throws a fatal SyntaxError. Your script will fail to load completely, breaking page functionality.	Add the matching closing bracket where your function ends.
Accidental '=' inside if (x = y)	Warning	Sets x equal to y instead of checking if they match. Your 'if' condition will almost always run unexpectedly.	Change single '=' to '===' for comparison.
Loose equality '==' or '!='	Tip	JavaScript tries to guess data types (e.g. 0 == '' is true), which causes hidden bugs with numbers and text.	Use strict equality '===' or '!==' for safe comparisons.
Dangerous eval() statement	Warning	Executes raw text as code, creating major security holes and slowing down your page.	Use JSON.parse() or standard functions instead.
Leftover debugger; statement	Warning	Freezes the screen whenever someone visits your site with browser developer tools open.	Delete 'debugger;' before publishing your code.
Duplicate object keys { id, id }	Warning	The second value silently overwrites the first one, which almost always points to a copy-paste mistake.	Give each property a unique name.
Test console.log() statements	Tip	Leaves temporary testing messages visible in your visitors' browser console.	Clean up test logs before deploying live.

🎨

Need to check CSS stylesheets as well?

Audit CSS styles for unclosed braces, invalid properties, and typos 100% locally.

Launch CSS Validator →

Frequently Asked Questions

Is my JavaScript code uploaded or stored on any server? ▼

What is the difference between an Error and a Warning? ▼

Why does it suggest using '===' instead of '=='? ▼

Can I validate custom code from Shopify, WordPress, or Webflow? ▼

Can I check JavaScript files without installing anything? ▼