Javascript - Map function (Functional programming)

1 - About

The functional programming function map in a Javascript context is only an array method as all functional programming javascript method.

For the map data type, see Javascript - Map Data Type

3 - Example

3.1 - Arrow Function

With an Arrow function as argument

  • Letters that we want to lowercase

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


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()));

3.2 - 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];


// 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);

4 - Documentation / Reference


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