Understanding Currying in JavaScript

Background: In React projects using Ant Design forms, validating passwords and account inputs often requires passing regex and values repeatedly, which is cumbersome.

Currying transforms a multi‑parameter function into a series of single‑parameter functions, enabling partial application and reuse.

Simple example: a sum function curried allows calling sumFn(1)(2)(3) to get 6.

const sumFn = x => y => z => x + y + z;

Benefits include single responsibility, easier maintenance, reduced duplication, and increased flexibility.

Practical currying utility:

const curryCheck = reg => txt => reg.test(txt);

Using it, account and password validators become checkAccount = curryCheck(accountReg) and checkPassword = curryCheck(passwordReg).

Another use case: logging with fixed date:

const logFn = date => type => msg => console.log(`${date.getHours()}:${date.getMinutes()} ${type} - ${msg}`);

A generic self‑curry function can convert any function:

const selfCurryFn = fn => { const len = fn.length; return function curry(...args) { return args.length >= len ? fn.apply(this, args) : (...args2) => curry.apply(this, args.concat(args2)); }; };

In Redux, middleware uses currying via applyMiddleware and compose to enhance store.dispatch.

Function composition (compose) combines multiple functions so they can be called in sequence, reducing repetitive calls.

const compose = (...fns) => (...args) => fns.reduceRight((res, f) => f.call(this, res), args);

Conclusion: Currying lets programmers fix some arguments, create specialized new functions, and build powerful abstractions through composition.