JavaScript Interview Question #180

What is function composition?

Advanced JavaScript, Practical Problems & Senior Interview Scenarios Senior Advanced

Quick Interview Answer

Function composition combines smaller functions so the output of one becomes the input of another. It encourages small focused transformations that can be tested independently and assembled into more complex behavior.

Detailed Explanation

Composition is particularly useful for validation, formatting, data transformation, and reusable processing pipelines.

Code Example

const trim = value => value.trim();
const lower = value => value.toLowerCase();
const addPrefix = value => `user:${value}`;

const compose = (...functions) =>
    value => functions.reduceRight(
        (result, fn) => fn(result),
        value
    );

const normalize =
    compose(addPrefix, lower, trim);

console.log(normalize(" ASIF "));
// user:asif