Partially apply a function

Fix the first arguments now and pass the rest later.

JavaScriptNode.js & browsers Version 1.0.0 · MIT · .md

function partial(fn, ...preset) { return (...rest) => fn(...preset, ...rest); }

Usage

const greet = (greeting, name) => greeting + ', ' + name;
partial(greet, 'Hello')('Ana'); // → 'Hello, Ana'

Lines marked → were executed in Node.js 22 and in headless Chromium, and each result was compared with the value shown. Lines marked e.g. are illustrative.

Know the limits

• fn.bind(null, …preset) is the built-in equivalent for functions that do not use this.

The function above is the code the usage lines run. It does not validate its arguments; add checks where it receives untrusted input.

Keep exploring

• Logical xor operator — True when exactly one of two values is truthy.
• Identity function — Return the argument unchanged.
• Box handler — Chain transformations on a value, then unwrap the result.