ES Modules

2 articles

JavaScript 19 Sep 2026 5 min read

How Node.js Chooses Between .mjs, .cjs, and .js Module Formats

Node.js can execute JavaScript through two module systems: ECMAScript modules (ESM) and CommonJS. The filename is one of the signals that selects between them, which is why files such as postcss.config.mjs appear in projects even when most source files still end in .js. The important detail is that .mjs is not a different JavaScript language. It is an explicit instruction to Node.js: parse and load this file as an ES module.

JavaScript Node.js

JavaScript 01 Sep 2026 3 min read

Use JavaScript Import Maps for Browser Module Aliases

Native ES modules normally require browser-resolvable URLs such as ./math.js or /vendor/lib.js. Import maps add a controlled indirection layer so application code can use stable bare specifiers such as app/config without a bundler rewriting imports. Define a map before modules load <script type="importmap"> { "imports": { "app/": "/js/app/", "vendor-utils": "/vendor/utils-v3.js" } } </script> <script type="module" src="/js/main.js"></script> Then /js/main.js can use:

JavaScript Import Maps