Higher Order Function

Functions can be data too !!!
Pass them as data like boolean, number, string and Array. 

const isEven = (num) => num % 2 === 0;  // here "function" is assigned to variable "isEven" 
const result = [1, 2, 3, 4].filter(isEven); // here function "isEven" is passed as an argument.

console.log({ result }); // { result: [ 2, 4 ] }

***A function that takes and/or returns another function is called a higher-order function. 
It’s “higher-order” because it operates on functions besides basic data types.***