The Ultimate Guide to Function Currying in JavaScript

If you've spent time in the functional programming world or looked at the source code of libraries like Redux, you’ve likely encountered functions that look like this: const result = add(5)(10)(20); . At first glance, it looks like a typo. But it’s actually one of the most powerful patterns in JavaScript: Function Currying. 1. What is Currying? (The Technical Definition) Currying is a functional programming technique where a function that takes multiple arguments is transformed into a sequence of nesting functions, each taking a single argument . Instead of: f(a, b, c) You get: f(a)(b)(c) Currying doesn’t actually call a function; it transforms it. The execution only happens once the last argument in the chain is provided. 2. How it Works: The Magic of Closures Currying is only possible in JavaScript because of Closures . When the outer function is called, it returns the inner function. Even after the outer function has finished executing, the inner function "remembers" the variables i