Callbacks and Higher-Order Functions

const numbers = [1, 2, 3, 4];
const doubled = numbers.map(function(num) {
  return num * 2;
});
console.log(doubled);

[1, 2, 3, 4]
[2, 4, 6, 8]
The output is [2, 4, 6, 8]. The map() method creates a new array populated with the results of calling a provided function on every element in the calling array. In this example, each number in the original array is multiplied by 2. map() is a higher-order function because it takes a callback function as an argument. This callback is executed for each element in the array, transforming the array without mutating the original.
[1, 4, 9, 16]
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