Compose functions from left to right

Build one function that passes a value through each function in order.

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

function pipe(...fns) { return input => fns.reduce((value, fn) => fn(value), input); }

Usage

const lowercase = text => text.toLowerCase();
const capitalize = text => text.charAt(0).toUpperCase() + text.slice(1);
const reverse = text => [...text].reverse().join('');
pipe(lowercase, capitalize, reverse)('HELLO'); // → 'olleH'
pipe()('unchanged'); // → 'unchanged'

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

• Functions run in the order listed. With no functions, the input comes back unchanged.
• Each step receives one value. For async steps, use a for…of loop with await.

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.