Curry a function

Collect arguments across calls until the function has as many as it declares.

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

function curry(fn, ...args) { return fn.length <= args.length ? fn(...args) : (...more) => curry(fn, ...args, ...more); }

Usage

const sum = (a, b, c) => a + b + c;
curry(sum)(1)(2)(3); // → 6
curry(sum, 1)(2, 3); // → 6
curry(sum, 1, 2, 3); // → 6

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

• The arity comes from fn.length, which stops at the first default or rest parameter: (a, b = 1) => … has length 1.
• The original used curry.bind(null, …); the closure is equivalent.

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.