How to Curry Function in JavaScript: Simple Guide and Examples

To curry a function in JavaScript, you create a new function that takes one argument at a time and returns another function until all arguments are received. Use nested functions or arrow functions to return these intermediate functions, allowing partial application of arguments with currying.

Syntax

Currying transforms a function with multiple arguments into a sequence of functions each taking a single argument.

The general syntax uses nested functions or arrow functions returning another function until all arguments are collected.

javascript

const curriedFunction = arg1 => arg2 => arg3 => {
  // function body using arg1, arg2, arg3
  return result;
};

Example

This example shows a curried function that adds three numbers by taking one argument at a time.

javascript

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

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

Output

6

Common Pitfalls

One common mistake is calling the curried function with all arguments at once instead of one by one, which will not work as expected.

Another is forgetting to return the inner function, which breaks the chain.

javascript

/* Wrong way: all arguments at once */
const addWrong = a => b => c => a + b + c;
// addWrong(1, 2, 3) // undefined or error

/* Right way: call one argument at a time */
const addRight = a => b => c => a + b + c;
console.log(addRight(1)(2)(3)); // 6

Output

6

Quick Reference

• Currying breaks a function into unary functions.
• Each function takes one argument and returns another function.
• Final function returns the result.
• Use arrow functions for concise syntax.

Key Takeaways

Currying transforms a multi-argument function into a chain of single-argument functions.

Always return the next function to continue the chain.

Call curried functions one argument at a time, not all at once.

Arrow functions make currying syntax clean and readable.

Currying helps create reusable and partially applied functions.