Currying

Currying is a functional programming technique where a function with multiple arguments is transformed into a sequence of functions, each of which takes one argument.

It allows creating partially applied functions and increases code reusability.

Technical Explanation

Currying transforms a function of the type:

f(a, b, c) → f(a)(b)(c)

Each call returns a new function that expects the next argument.

When all parameters are passed, the original function body is executed.

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

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

multiply(2) returns an internal function that remembers the value a = 2 and waits for b.

This is achieved through a closure — the internal function maintains access to the variables of the external one.

Currying Application

• Partial application

  You can fix some of the arguments in advance and reuse the function:

  const add = a => b => a + b;
  const add10 = add(10);
  add10(5); // 15

• Function Composition

  Simplifies combining small pure functions into complex chains.

• Logic Reuse

  Allows creating specialized functions from universal templates.

Key Ideas

• Currying creates a chain of functions, each returning a new one until all arguments are applied.
• Based on closures, which preserve the argument context.
• Simplifies the composition and reuse of functions.
• Often used in functional programming and libraries like Lodash, Ramda.