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Is once ESM-only? Can you require() it?

Run a function exactly one time

Last verified Sep 9, 2026 against once@1.4.0. Markdown · JSON

CommonJS CommonJS — require() works on every Node.js version we test

once ships CommonJS only. require("once") works on every Node.js version we test (18, 20, 22, 24 and 26) and in Bun. import "once" also works because Node.js and Bun can import CommonJS from ES modules, but only the default export is guaranteed; named imports depend on Node's static analysis of the module.

What to do

  1. require("once") works on every Node.js version we test (18, 20, 22, 24 and 26) and in Bun.
  2. From ES modules use the default import: import once from "once"; then destructure. Named imports only work when Node.js can statically detect the exports.
  3. TypeScript: npm install -D @types/once
Latest
1.4.0 (Sep 6, 2016)
Module format
CommonJS
Last CommonJS version
1.4.0
TypeScript types
@types/once
Node engines
not declared
Weekly downloads
109.6M
License
ISC

Does once@1.4.0 actually load? Runtime test results

Installed and executed on Sep 9, 2026 with require("once") from a CommonJS file and import "once" from an ES module.

Runtimerequire("once")import "once"
Node.js 18✓ works✓ works
Node.js 20✓ works✓ works
Node.js 22✓ works✓ works
Node.js 24✓ works✓ works
Node.js 26✓ works✓ works
Bun 1.4.0✓ works✓ works

How to import once

ES modules (import)

import once from "once";

Named imports from a CommonJS package only work when Node.js can statically detect them. If a named import fails, use the default import and destructure.

CommonJS (require)

const once = require("once");

Module format by version

Derived from the type, main and exports fields of every stable release on npm, corrected where a runtime test of that version contradicted them (7 versions; the newest 7 shown).

VersionsFormatFirst published
1.1.1 – 1.4.0CommonJSAug 14, 2012

Frequently asked

Is once ESM-only?

once@1.4.0 is a CommonJS package. once ships CommonJS only. require("once") works on every Node.js version we test (18, 20, 22, 24 and 26) and in Bun. import "once" also works because Node.js and Bun can import CommonJS from ES modules, but only the default export is guaranteed; named imports depend on Node's static analysis of the module.

Can I import once with ES module syntax?

Yes. import once from "once" works in Node.js and Bun because they support importing CommonJS modules. Named imports work only when Node.js can statically detect the exports.

Does once work in Bun?

Yes. import "once" loaded successfully in Bun 1.4.0 on Sep 9, 2026.

Does once ship TypeScript types?

Not bundled. Install the community types with "npm install -D @types/once".

Links

Other commonjs packages

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