A Map in Javascript holds key-value pairs where the keys can be any datatype.
How to Create a Map?
We can create a map as shown below.
a) By passing an Array to new Map()
const cities = new Map([
["Nagpur", "Nag"],
["Mumbai", "Mum"],
["Delhi", "Del"]
]);
b) Create a Map and use Map.set()
const cities = new Map();
cities.set("Nagpur", "Nag");
cities.set("Mumbai", "Mum");
cities.set("Delhi", "Del");
What are avaialble Map methods?
1) new Map() : Creates a new Map object
2) set() : Sets the value for a key in a Map
ex: cities.set("Kolkata", Kol);
3) get() : Gets the value for a key in a Map
ex: cities.get("Kolkata");
4) clear() : Removes all the elements from a Map
5) delete() : Removes a Map element specified by a key
6) has() : Returns true if a key exists in a Map
7) forEach() : Invokes a callback for each key/value pair in a Map
const cities = new Map([
["Nagpur", "Nag"],
["Mumbai", "Mum"],
["Delhi", "Del"]
]);
cities.forEach (function(value, key) {
let text = "";
text += key + ' = ' + value
console.log(text);
})
Output:
Nagpur = Nag
Mumbai = Mum
Delhi = Del
8) entries() : Returns an iterator object with the [key, value] pairs in a Map
const cities = new Map([
["Nagpur", "Nag"],
["Mumbai", "Mum"],
["Delhi", "Del"]
]);
for (const x of cities.entries()) {
let text1 = "";
text1 += x ;
console.log(text1);
}
Output:
Nagpur,Nag
Mumbai,Mum
Delhi,Del
9) keys() : Returns an iterator object with the keys in a Map
// Create a Map
const cities = new Map([
["Nagpur", "Nag"],
["Mumbai", "Mum"],
["Delhi", "Del"]
]);
for (const x of cities.keys()) {
let text1 = "";
text1 += x ;
console.log(text1);
}
Output:
Nagpur
Mumbai
Delhi
10) values() : Returns an iterator object of the values in a Map
// Create a Map
const cities = new Map([
["Nagpur", "Nag"],
["Mumbai", "Mum"],
["Delhi", "Del"]
]);
for (const x of cities.values()) {
let text1 = "";
text1 += x ;
console.log(text1);
}
Output:
Nag
Mum
Del
11) size : The size property returns the number of elements in a Map
ex: cities.size
