javascript Map object vs Set object

Question

JavaScript Map and Set objects are both iterable objects. Both store object by [key, value] pair. I want to know when to use what? Is there any preference one over

Answer 1

There are two main data structures:

• Objects: are used for storing keyed collections.
• Arrays: are used for storing ordered collections.

But that’s not enough for real life. That’s why Map and Set also exist.

• Map: is a collection of keyed data items, just like an Object. But the main difference is that Map allows keys of any type.

For instance:

let map = new Map();

map.set('1', 'str1');   // a string key
map.set(1, 'num1');     // a numeric key
map.set(true, 'bool1'); // a boolean key


let hamid = { name: "Hamid" };
// john is the key for the map
map.set(hamid, 123);

• Set : is a special type collection – “set of values” (without keys), where each value may occur only once.

instance:

let set = new Set();

let hamid= { name: "Hamid" };
let pete = { name: "Pete" };
let mary = { name: "Mary" };

// visits, some users come multiple times
set.add(hamid);
set.add(pete);
set.add(mary);
set.add(hamid);
set.add(mary);

// set keeps only unique values
alert( set.size ); // 3
 

https://javascript.info/map-set