# JavaScript Viewer

Free online JavaScript viewer. Open .js, .mjs, .cjs, and .jsx files directly in your browser without uploading them.

> Canonical page: https://elysiatools.com/en/viewers/js

- **Category:** Text Files

- **Supported formats:** .js, .mjs, .cjs, .jsx

## Overview

This JavaScript viewer renders source files locally in your browser. JavaScript powers web interactivity, servers (Node.js), and UI components (React/JSX). Pick a sample or choose your own .js file to inspect functions, modules, and syntax with highlighting.

## When to use

- You have a JavaScript file and want to read it without an editor.
- You need to inspect an ES module (.mjs) or JSX component quickly.
- You are on a device without a code editor and need to browse a .js file.

## How it works

- Select a built-in sample or choose your own .js, .mjs, .cjs, or .jsx file.
- The viewer renders the source with syntax highlighting in the browser, with no upload.
- Inspect the code, then switch samples or load another file any time.

## Use cases

- Reviewing ES modules, scripts, and Node.js files.
- Inspecting React/JSX component sources.
- Browsing JavaScript code on any device.

## Samples

- **JavaScript Mixed Comments**: JavaScript file with single-line, multi-line comments, URLs, and shebang
- **JavaScript Invalid Variable Names**: JavaScript code demonstrating invalid variable names including numbers at start, special characters, and reserved keywords
- **Real World Refactoring Cases**: JavaScript code with real-world refactoring examples showing beginner mistakes, naming issues, and before/after comparisons
- **Simple JS Module**: A minimal ES module with a function, array map, and exports
- **Fetch Example (.mjs)**: An ES module (.mjs) using async/await fetch with error handling
- **React Component (.jsx)**: A small React counter component written in JSX

## Frequently asked questions

### Is this JavaScript viewer free?

Yes. It runs in your browser for free and needs no registration or installation.

### Are my JavaScript files uploaded?

No. Files opened from your device stay on your device. Only public sample files come from the server.

### Does it support .mjs, .cjs, and .jsx?

Yes. The viewer reads .js, .mjs, .cjs, and .jsx extensions equally.

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