JavaScript only has a map which is equivalent to unordered map

by Jii Yoo
…
Note
|
Writing

C++ provides two different map data structures: unordered_map and map (Difference between unordered_map and map).

unordered_map is typically faster than the map especially when accessing elements because it is implemented using a hash map internally. Also it remembers the original insertion order of the keys.

JavaScript only provides a Map data structure which acts similary to unordered_map. It remembers the original insertion order of the keys, it has an average of constant time or logarithmic time look up depending on the interal implementation: hash table or tree.

const map1 = new Map();

map1.set('a', 1);
map1.set('c', 3);
map1.set('b', 2);

map1; // Map {'a': 1, 'c': 3, 'b': 2 }

map1.set('a', 97);
map1.get('a'); // 97
map1.size; // 3

map1.has('a'); // true
map1.hash('foo'); // false

Cool thing about the map in JavaScript is that we can use anything for the key including a function and an object.

const map1 = new Map();

const func = () => {console.log('function')}
const obj = {
    'a': 97,
    'b': 98
};

map1.set(func, 'this is a function');
map1.set(obj, 'this is an object')

map1.get(func); // 'this is a function'
map1.get(obj); // 'this is an object'
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