Box handler

Chain transformations on a value, then unwrap the result.

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

function boxHandler(value) { return { next: f => boxHandler(f(value)), done: f => f(value) }; }

Usage

const percent = text => boxHandler(text).next(t => t.replace('%', '')).next(Number.parseFloat).done(n => n * 0.01);
percent('50%'); // → 0.5
percent('12.5%'); // → 0.125

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

• Each next returns a new box; nothing is mutated. An error thrown in a step propagates immediately.
• For steps that do not need the box, a pipe reads the same; see Compose functions from left to right.

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.
• Check if a value is a function — True for anything callable: functions, arrows, async and generator functions, classes.