Does the sample script do anything when loaded?

No. It defines an array and two functions and has no side effects.

What is the MIME type of a JS file?

The MIME type is text/javascript. The file extension is .js.

Is a sample JS file the same as a dummy or example JS file?

Yes. Sample, test, dummy and example JS files are different names for the same thing: a JS file with known contents that stands in for a real one. Any file on this page will do wherever a tutorial or a test plan asks for a dummy JS file.

Free JS sample files

JavaScript source code, as loaded by browsers and run by Node.js. Download valid JS test files in 4 exact sizes, from 1 KB to 1 MB, each with a checksum.

Extension: .js
MIME type: text/javascript
Kind: Text
Category: Code

JS files by size

Every file below is a valid JavaScript source file file of exactly the stated size. Open a file's page for its checksum and contents, and to preview it in your browser before downloading.

JS sample files by size
File	Size	Contents	Download
1 KB JS samplesample-js-1kb.js	1 KB1,024 bytes	Array entries: 4	Download JS
10 KB JS samplesample-js-10kb.js	10 KB10,240 bytes	Array entries: 81	Download JS
100 KB JS samplesample-js-100kb.js	100 KB102,400 bytes	Array entries: 833	Download JS
1 MB JS samplesample-js-1mb.js	1 MB1,048,576 bytes	Array entries: 8,427	Download JS

What is a JS file?

A .js file contains JavaScript, the programming language of the web. Browsers download and execute it, and runtimes such as Node.js, Deno and Bun run it on servers.

The language is standardised as ECMAScript, with a new edition each year.

How to recognise a JS file

No signature bytes. JS files are identified by parsing their content.

Extension	.js
MIME type	text/javascript
Standard	ECMA-262 (ECMAScript)
MIME type	text/javascript, per RFC 9239
Encoding	UTF-8
Module systems	ECMAScript modules and CommonJS

What to test for

These are the behaviours that most often go wrong when software handles JS files.

The old types application/javascript and application/x-javascript are obsolete; text/javascript is the registered type.
Never execute an uploaded script. Treat .js uploads as text to be stored or analysed.

Strengths of JS

Runs in every browser with no build step required.
One language for browsers, servers and tooling.

Limitations of JS

A single syntax error stops the whole file from running.
Large scripts delay page interactivity while they parse and execute.

Typical uses of JS test files

Testing bundlers and minifiers with large inputs
Checking syntax highlighters and editors
Testing static asset delivery and caching

Software that opens JS

All web browsers
Node.js, Deno and Bun
esbuild, webpack, Rollup and Terser

Specifications

JS sample files: questions

Does the sample script do anything when loaded?: No. It defines an array and two functions and has no side effects.
What is the MIME type of a JS file?: The MIME type is text/javascript. The file extension is .js.
Is a sample JS file the same as a dummy or example JS file?: Yes. Sample, test, dummy and example JS files are different names for the same thing: a JS file with known contents that stands in for a real one. Any file on this page will do wherever a tutorial or a test plan asks for a dummy JS file.