canirequire › CommonJS › once
Is once ESM-only? Can you require() it?
Run a function exactly one time
Last verified Sep 9, 2026 against once@1.4.0. JSON
CommonJS CommonJS — require() works on every Node.js version
once ships CommonJS only. require("once") works everywhere. 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.
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.
| Runtime | require("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 | ✓ 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 (7 versions; the newest 7 shown).
| Versions | Format | First published |
|---|---|---|
| 1.1.1 – 1.4.0 | CommonJS | Aug 14, 2012 |
Frequently asked
Is once ESM-only?
once@1.4.0 is a CommonJS package. once ships CommonJS only. require("once") works everywhere. 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 on Sep 9, 2026.
Does once ship TypeScript types?
Not bundled. Install the community types with "npm install -D @types/once".
Links
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