What Is a .mjs File? .mjs Format, MIME & How to Open

Quick facts

Extension.mjs

File typeJavaScript Module

MIME typetext/javascript

CategoryData & Text

CharsetUTF-8

CompressibleYes

Format familyjavascript

What is .mjs

What is a .mjs file?

A .mjs file is a JavaScript Module — ES module JavaScript file.

In the mime-db registry it maps to text/javascript with UTF-8 encoding, and it is marked as compressible. When serving .mjs over HTTP, set the Content-Type header as shown in Developer info below.

Related entities: it maps to text/javascript and is used by JavaScript among others — and is delivered over HTTP via the Content-Type header.

How to open .mjs files

Use VS Code or Node.js to open and edit .mjs files.
Any text editor (Notepad, VS Code) can inspect the raw content as text.

Developer info

When served over HTTP, responses should set the following header:

Content-Type: text/javascript; charset=utf-8

Common software that reads/writes .mjs:

VS CodeNode.js

Relation chain

.mjsextension of

format

javascriptserved as

mime type

text/javascriptsent via header

http header

Related extensions

Related MIME types

Related programming languages

JavaScript

.js ._js .bones

Common uses

Configuration files
Data interchange between systems
API request and response payloads
Logs and data exports

How to edit .mjs files

Open the file with VS Code, make your changes and save.
Most editors preserve the original formatting and encoding — avoid changing the charset.

How to create .mjs files

Create a new file and save it with the .mjs extension, or export this format from VS Code.

Frequently asked questions

What programs can open .mjs files?

Common options include VS Code, Node.js. You can also open many of these files with built-in viewers or a browser.

How do I create a .mjs file?

Create a new file in any text editor or the app that owns the format and save it with the .mjs extension.

What is the relationship between .mjs and the text/javascript MIME type?

text/javascript is the media type identifier used for .mjs files during network transfer (for example in the HTTP Content-Type header).

Sources & standards

Updated 2026-08-18

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