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Map object in javascript

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Map object in javascript

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Ajay
·

2 min read

Map object is used to store data in key-value pairs. It also maintains the order of insertion of elements into the map.

let m = new Map();
m.set("name", "Karl");

Map methods

// DECLARE A MAP OBJECT
let m = new Map();

//INSERT ELEMENT INTO MAP
m.set("name", "Karl");
m.set("age", 25);

console.log(m); // {name:'Krl', age: 25}

// ACCESS ELEMENT OF MAP
m.get("name"); // "Karl"
m.get("age"); // 25

//CHECK IF A KEY EXISTS IN THE MAP
m.has("name"); // true
m.has("phone"); // false

// DELETE AN ELEMENT
m.delete("age"); // true
m.delete("address"); // false => address key doesn't exist on map

// GET THE SIZE OF MAP
m.size(); // output: 2

Iterate map object

There are cases when we need to iterate a map object just like we iterate an array.

We can iterate a map object by:

  • Using for...of loop.

  • Using for...each loop

    for...of loop

    let m = new Map();

m.set(1, "Batman");
m.set(2, "Spiderman");
m.set(3, "Ironman");

for(const [key, val] of m){
    console.log(key + " = " + val);
}
// 1 = Batman
// 2 = Spiderman
// 3 = Ironman

// ITERATING KEYS
for(cont key of m.keys()){
    console.log(key);
}
// 1
// 2 
// 3

// ITERATING VALUES
for(cont val of m.values()){
    console.log(val);
}
// Batman
// Spiderman
// Ironman

    forEach loop

    let m = new Map();
m.set(1, "Batman");
m.set(2, "Spiderman");
m.set(3, "Ironman");

m.forEach((val, key) =>{ // Note: key is second parameter.
    console.log(key + " = " + val);
});
// 1 = Batman
// 2 = Spiderman
// 3 = Ironman

Convert a map into a 2D array

It's super easy to convert a map into a 2D array. We can use a spread operator or Array.from() method.

let m = new Map();
m.set(1, "Batman");
m.set(2, "Spiderman");
m.set(3, "Ironman");

// using spread operator
let 2dArr = [...m];
console.log(2dArr); // [[1, 'Batman'],[2, 'Spiderman'],[3, 'Ironman']]

// using Array.from() method
let 2dArr = Array.from(m);
console.log(2dArr);//[[1, 'Batman'],[2, 'Spiderman'],[3, 'Ironman']]

Convert a 2D array into a map

We need to pass a 2D array as an argument into the map constructor function.

let 2dArr = [[1, 'Batman'],[2, 'Spiderman'],[3, 'Ironman']];

let m = new Map(2dArr);

console.log(m); // {1: 'Batman',2: 'Spiderman',3: 'Ironman',}

I hope you found this article helpful.

JavaScript