Higher-Order Functions

Introduction

This year I set out to learn a new programming language just for fun and I’ve always been curious about web development so I chose JavaScript.

In the first few weeks I learned about syntax, DOM, primitive values, objects, scope, etc. but one thing that caught my attention was the concept of Higher Order Functions.

Disclaimer: maybe you use it but you didn’t know the name.

Higher-Orders Functions

What is a Higher-Order Function?

In mathematics and computer science a higher-order function is a function that does at least one of the following:
Take one or more function as argument.
Return a function.

How is that possible?

Well this happen because the functions are considerer as First Class Objects that meaning that the functions are consider as objects and they can do anything an object do.

The properties of a first class functions:

A function is an instance of the Object type.
You can store the function in a variable.
You can pass the function as a parameter to another function.
You can return the function from a function.
You can store them in data structure such as hash, tables, list, …

Why are importants?

Well, higher order functions simplify our code and keep it DRY. Let’s do some examples to demonstrate this.

first order function

Suppose we have the copyArrayAndAddOne function that copy and array of integer and add 1 to each element.

function copyArrayAndAddOne(array) {
    const output = [];
    for (let i=0; i < array.length; i++){
        output.push(array[i] + 1);
    }
    return output
}
const myArray = [1, 2, 3];
const result = copyArrayAndAddOne(myArray);

What if now we want to copy array and rest by 1.

function copyArrayAndRestOne(array) {
    const output = [];
    for (let i=0; i < array.length; i++){
        output.push(array[i] - 1);
    }
    return output
}
const myArray = [1, 2, 3];
const result = copyArrayAndRestOne(myArray);

What if now we want a function copyArrayAndMultiplyByThree?

Well in that case we need to write the function and add the new operation, at this point we may start to notice that our functions repeat a lot of code and we just need to change the operation symbol.

That meaning we are breaking the DRY principle.

Higher Order Functions

We could generalize our function, lets check how.

function copyArrayGeneral(array, callback){
    const output = [];
    for(let i=0; i<array.length; i++){
        output.push(callback(array[i]));
    }
    return output;
}

for out first two function we can now use copyArrayGeneral:

function multiplyByThree(input) { return input * 3 };
const result = copyArrayGeneral([1, 2, 3], multiplyByThree)

function addOne(input) { return input + 1 };
const result = copyArrayGeneral([1, 2, 3], addOne)

Final Thoughts

Higher order functions are present in other programming languages such as Python and are useful because we can use them to write code with fewer errors and better to understand, finally they help you to be a fast programmer because you can reuse your code. This type of programming is know as functional programming.

Introduction#

Higher-Orders Functions#

What is a Higher-Order Function?#

How is that possible?#

Why are importants?#

first order function#

Higher Order Functions#

Final Thoughts#