Higher-order functions for Arrays in Javascript

If you are learning JavaScript, you must have come across the term Higher-Order Functions.

Higher-Order Functions are extensively used in JavaScript. If you have been programming in JavaScript for a while, you may have already used them without even knowing.

List of Higher-order functions in Javascript

1. forEach
2. Map
3. Filter
4. Reduce
5. Some
6. Sort

Higher-order functions will allow you to write code using Functional approach, so that you will no longer need to use Imperative for/while loops to process arrays

Let’s take a look at some examples of built-in higher-order functions and see how it compares to solutions where we aren’t using Higher-Order Functions.

Let's use the below array, it contains the country and country code.

let arrayCollection = [{country:"United States",countryCode:1},
                      {country:"Canada",countryCode:1},
                      {country:"Russia",countryCode:7},
                      {country:"Switzerland",countryCode:41},
                      {country:"Brazil",countryCode:55},
                      {country:"Malaysia",countryCode:60},
                      {country:"Singapore",countryCode:65},
                      {country:"Japan",countryCode:85},
                      {country:"India",countryCode:91},
                      {country:"North Korea",countryCode:850}];
let arrayCollection1 = [];

without Higher order function

for(let i=0;i<arrayCollection.length;i++){
  arrayCollection1.push(arrayCollection[i].country);
}

 1. forEach

forEach is run the given function of each array element

In our example, we will copy the name of the countries and push it into the new array(arrayCollection1)

arrayCollection.forEach(country => {
    arrayCollection1.push(country.country);
});

The higher order code is very simple compared to the normal for loop

2. Map

The map method is creating a new array with the result and return it.

let arrayCollection1 =  arrayCollection.map(val => val.country);
console.log(arrayCollection1);