Higher order functions and callbacks

In a nutshell, higher-order functions are those functions that take other functions as arguments OR return other functions. The function passed as arguments in higher-order function is known as a callback.

JavaScript has some built-in higher-order functions such as map(), filter() and reduce().

map()

const numArray = [1, 5, 3, 6, 4, 7]; 
const increasedArray = numArray.map((element) => {
    return element + 1; 
});
 console.log(increasedArray); // [2, 6, 4, 7, 5, 8]

filter()

let arr [1,2,3,4,5];
const resultant Array = arr.filter((element ) => {
    return element > 3; 
})
console.log(resultantArray); // [4, 5]

reduce()

const numArray = [1, 2, 3, 4, 5];
const sum = numArray.reduce((total, num) => {
    return total + num; 
});
console.log(sum);

Callbacks are nothing more that functions, that are passed as arguments to other functions.

Using the previous filter example…

let arr [1,2,3,4,5];
const resultant Array = arr.filter((element) => {return element>3})
console.log(resultantArray); // [4, 5]

… this would be the callback function we’re passing as an argument to the filter() higher order function.

(element) => {return element>3}