JavaScript · The language round

What is currying and how is it different from partial application?

MediumfunctionscurryingclosuresUpdated Oct 2026

Short answer

Currying turns a function of several arguments into a chain of one-argument functions. Partial application fixes some arguments now and supplies the rest later. Both rely on closures.

The terms are often used interchangeably, but they describe different transformations. Currying is about the shape of the function. Partial application is about pre-filling arguments.

const add = (a) => (b) => (c) => a + b + c;

console.log(add(1)(2)(3)); // 6

function multiply(a, b) {
  return a * b;
}

const double = multiply.bind(null, 2);
console.log(double(5)); // 10

add is curried. double is a partially applied version of multiply.

A reusable curry helper

function curry(fn) {
  return function curried(...args) {
    if (args.length >= fn.length) {
      return fn.apply(this, args);
    }

    return (...next) => curried.apply(this, [...args, ...next]);
  };
}

const addThree = curry((a, b, c) => a + b + c);
console.log(addThree(1)(2)(3)); // 6
console.log(addThree(1, 2)(3)); // 6

Currying always produces unary functions in the strict sense
Partial application can fix any number of arguments at once
Both create new functions through closures
bind is a built-in form of partial application

Currying is useful when you want to compose functions or create specialised versions of a general function. It is not automatically better than a normal multi-argument function.

Follow-ups you should expect

Interviewers use these to check whether the first answer was understanding or memorisation.

1What is the difference between currying and partial application?
2How does `bind` perform partial application?
3How would you implement a generic `curry` function?
4Where is currying useful in real code?

Say it in the interview

Currying transforms a function that takes several arguments into a chain of functions that each take one argument. Partial application fixes some arguments now and leaves the rest for later. Both use closures. bind is a built-in partial application. I use currying when I want composable functions or specialised versions, but I do not force it when a normal function is clearer.

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A reusable curry helper

Follow-ups you should expect

Related questions

Now say it out loud.