What Is Currying? – Definition, Meaning & Examples of Curried Functions

Currying means converting a function with multiple arguments to a series of functions with only one argument each.

Example of Currying in JavaScript

Consider the following code:

// Define an un-curried senseOrgans function:
function senseOrgans(s1, s2, s3, s4, s5) {
  return `The 5 basic senses are the ${s1}, ${s2}, ${s3}, ${s4}, and ${s5}.`;
}

// Invoke the senseOrgans() function:
senseOrgans("eye", "nose", "ear", "mouth", "skin");

// The invocation above will return:
// "The 5 basic senses are the eye, nose, ear, mouth, and skin."

Try Editing It

The senseOrgans() function above is an un-curried function with five (5) arguments. You can turn it into a curried function by converting it into a sequence of functions with only one argument each.

// Define a curried senseOrgans function:
function senseOrgans(s1) {
  return function (s2) {
    return function (s3) {
      return function (s4) {
        return function (s5) {
          return `The 5 basic senses are the ${s1}, ${s2}, ${s3}, ${s4}, and ${s5}.`;
        };
      };
    };
  };
}

// Invoke the senseOrgans() function:
senseOrgans("eye")("nose")("ear")("mouth")("skin");

// The invocation above will return:
// "The 5 basic senses are the eye, nose, ear, mouth, and skin."

Try Editing It

The senseOrgans() function above is a curried function because we converted it from a function with multiple arguments to a series of functions with one argument each.

What Is the Advantage of Currying?

The primary advantage of a curried function is its flexibility. You can invoke a curried function without immediately supplying all its required arguments.

In other words, currying allows you to invoke a function in bits by storing each invocation's returned function in a variable. Then, you can invoke the returned function whenever its argument is available.

Here's an example:

// Invoke the senseOrgans() function:
const noseOrgan = senseOrgans("nose");

// Invoke the noseOrgan's function:
const eyeAndEarOrgans = noseOrgan("eye")("ear");

// Invoke the eyeAndEarOrgans' function:
const skinOrgan = eyeAndEarOrgans("skin");

// Invoke the function in the skinOrgan variable:
skinOrgan("mouth");

// The invocation above will return:
// "The 5 basic senses are the nose, eye, ear, skin, and mouth."

Try Editing It

Each variable in the example above contains a function initially returned from the senseOrgan() function.

Defining senseOrgan() as a curried function allowed us to invoke its returned functions at our own pace when we had the required arguments available.

Overview

Currying a function means converting a function of multiple arities (arguments) to a series of functions with one arity each.

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