Javascript - Map function (Functional programming)

Arrow Function

With an Arrow function as argument

• Letters that we want to lowercase

const letters = ['A', 'B', 'C', 'D', 'E'];

• The Array Map function ¹⁾ with an Arrow function as argument

console.log("Showing only the function value call");
const lowercases = letters.map((letter) => letter.toLowerCase());
console.log(lowercases);

• With the index

console.log("Showing the value, index call");
letters.map((letter, index) => console.log("Letter at position "+index+" is "+letter.toLowerCase()));

Function Declaration

With an Javascript - Function Declaration

• The function declaration

function double(num) {
    return 2*num;
}

• The array of number that we want to double.

const numbers = [1, 2, 3, 4, 5];

• The Array Map function

// Passing the function name
const doubled = numbers.map(double);
// Declaring the function inside the map works also
const doubled2 = numbers.map(function double(num) {
    return 2*num;
});
console.log("doubled data");
console.log(doubled);
console.log("doubled2 data");
console.log(doubled2);

Syntax

• Functional Form

myArray.map((element, index) => { ... });

• Procedural form

map((element, index, myArray) => { ... });