What is the difference between currying and partial application?

The short answer

Currying transforms a function into a chain of single-argument functions: f(a, b, c) becomes f(a)(b)(c). Partial application fixes some arguments upfront and returns a function for the rest: f(a, b, c) becomes g(c) where a and b are already set. Currying always produces unary functions, partial application can fix any number of arguments.

Side by side

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

// Currying — one argument at a time
const curried = (a) => (b) => (c) => a + b + c;
curried(1)(2)(3); // 6

// Partial application — fix some arguments upfront
const partial = add.bind(null, 1, 2);
partial(3); // 6

The key differences

CurryingPartial ApplicationArgumentsAlways one at a timeFix any number at onceResultChain of unary functionsOne function with fewer argumentsFlexibilityMust call step by stepPre-fill whatever you want

When to use which

Currying works well when you want to create a pipeline of transformations or when a library expects single-argument functions:

const add = (a) => (b) => a + b;
[1, 2, 3].map(add(10)); // [11, 12, 13]

Partial application works well when you want to create specialized versions of a function:

const log = (level, message) =>
  console.log(`[${level}] ${message}`);
const logError = log.bind(null, 'ERROR');
const logInfo = log.bind(null, 'INFO');

logError('Something broke'); // [ERROR] Something broke
logInfo('App started'); // [INFO] App started

In practice

In everyday JavaScript, partial application (often through bind or closures) is more common than currying. Currying is more common in functional programming libraries.

Why interviewers ask this

Many candidates confuse the two terms. Interviewers ask this to see if you understand the precise difference. It also tests your understanding of closures and higher-order functions.