Currying in JavaScript

June 24, 2020

What is Currying?

Many languages when it comes to the realm of functional programming make use of currying. It is the process of transforming a function that contains multiple arguments into a sequence of nested functions. There are several benefits of currying and one of the main ones is through the creation of utility functions. I find this very helpful when going back to code I haven’t seen in a while and being able to expand on a program as I made use of the process of currying.

The arguments of currying are kept because of closure & are consecutively used in execution until the final currying chain is returned. Currying can be a powerful concept in creating programs. In languages like Haskell, all functions are curried by default.

Example

Let’s take a look at a simple function that will take two arguments

const divide = (a, b) => a / b;

The two arguments (a & b) simply divide so therefore

divide(10, 5);
// returns 2

We can change this function to a curried version by separating the arguments…

const divideCurried = (a) => (b) => a/b;

Testing the following code

divideCurried(10)(5);
// returns 2

A curried utility function we can make use of

const divideCurriedBy10 = divideCurried(10);

Now we can make use of this new curried utility function to divide any number by 10

console.log(divideCurriedBy10(1));
// 10
console.log(divideCurriedBy10(50));
// 0.2

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