Simple Higher-order functions

A function can take a function as an argument or can return a function as a value is called a higher-order function.

1. A function that returns a function

const higherOrderFunc = function() {
    return function() {
        return 12;
    }
}

// which returns below function hence it is higher order function.
higherOrderFunc(); 
> ƒ () {
        return 12;
    }

higherOrderFunc()();
> 12

1. A function that takes a function as an argument

const testFunc = function(x) {
    return x + 12;
}

//which takes function as an argument.
const higherOrderFunc = function(testFunc) {
    return testFunc(8);
}

higherOrderFunc(testFunc);
> 20

Example: 1

function calculate(operation, numbers) {
    return operation(numbers);
}

function addition(numbers) {
    let sum = 0;
    for (const number of numbers) {
        sum+=number;
    }
    return sum;
}

function multiply(numbers) {
    let sum = 1;
    for (const number of numbers) {
        sum*=number;
    }
    return sum;
}

const numbers = [1,2,3,4,5];
console.log(calculate(addition, numbers));
> 15

console.log(calculate(multiply, numbers));
> 120

calculate(multiply, numbers) - Don't append parenthesis while sending function as an argument.

Benefits of higher-order functions:

1. Reduces code duplication
2. Single responsibility

In Javascript, functions can take arguments as primitives or objects and return the same called first-order functions.

JS built-in higher order functions are:

arr.reduce(), arr.forEach(), arr.filter(), arr.map()