What Is Currying in JavaScript?

What Is Currying in JavaScript?

Currying transforms a function with multiple arguments into a sequence of functions that each take one argument.

Example

// regular: f(a, b, c)
function add(a, b, c) { return a + b + c; }
add(1, 2, 3); // 6

// curried: f(a)(b)(c)
function curriedAdd(a) {
  return function (b) {
    return function (c) {
      return a + b + c;
    };
  };
}
curriedAdd(1)(2)(3); // 6

Generic curry Function

function curry(fn) {
  return function curried(...args) {
    if (args.length >= fn.length) return fn(...args);
    return (...next) => curried(...args, ...next);
  };
}
const sum = curry((a, b, c) => a + b + c);
sum(1)(2)(3); // 6
sum(1, 2)(3); // 6
sum(1)(2, 3); // 6

Use Cases

• Partial application: preset some arguments: const add5 = sum(1)(2); add5(3);
• Function composition: chain small functions.
• Reusable configurations: const log = curry((level, msg) => ...); const info = log("info");

The Takeaway

Currying transforms f(a, b, c) into f(a)(b)(c). Use the generic curry function with recursion. Use cases: partial application, composition, and configurable functions. Closures make currying possible (each returned function closes over previous arguments).