Currying vs partial application

JavaScriptMiddle~1 min read

Partial application and currying are indeed similar - both techniques let you pass arguments to a function partially. But there is a clear difference in essence and purpose between them.

1. Definitions

Currying

Transforms a function with n arguments into a chain of functions, each of which takes exactly one argument.

javascript

// Original function
function add(a, b, c) {
  return a + b + c;
}

// Curried version
const curriedAdd = a => b => c => a + b + c;

curriedAdd(1)(2)(3); // 6

Each call returns a new function that expects the next argument. Currying is a pure functional transformation of the signature.

Partial Application

Creates a new function with pre-set (partially applied) arguments, but does not change the number of arguments the function takes.

javascript

function add(a, b, c) {
  return a + b + c;
}

// Partially apply the first argument
const add1 = add.bind(null, 1);

add1(2, 3); // 6

Partial application simply fixes some of the arguments, and the rest can be passed later together.

2. The main difference

Criterion	Currying	Partial Application
What it does	Splits the function into a chain of one-argument functions	Fixes part of the original function's arguments
Arguments per step	1 argument per call	Several arguments can be passed at once
Returns	A function expecting one next argument	A function expecting the remaining arguments
Call example	`f(a)(b)(c)`	`f(a, b)(c)` or `f(a)(b, c)`
Purpose	Unifying calls and composition	Reusing a function with pre-set arguments

Example for clarity:

Currying:

javascript

const multiply = a => b => c => a * b * c;

multiply(2)(3)(4); // 24

Partial application:

javascript

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

const double = multiply.bind(null, 2); // fix a=2

double(3, 4); // 24

Summary:

Currying is a formal transformation of a function into a sequence of one-argument calls. Partial Application is a practical technique for pre-filling part of the arguments and passing the rest later.

Short Answer

Interview ready

Premium

A concise answer to help you respond confidently on this topic during an interview.