TypeScript Map

TypeScript Map is a new data structure introduced in ES6. A Map allows to store key-value pairs, similar to the maps in other programming languages e.g. Java or C#.

1. Creating a Map

Use Map type and new keyword to create a map in the TypeScript.

let myMap = new Map();

To create a Map with initial values, pass the values as an array to the Map constructor.

let myMap = new Map([
        ["key1", "value1"],
        ["key2", "value2"]
    ]); 

2. Add, retrieve, delete entries from Map

The common operations abailable over a Map are:

1. map.set() – method to add entries in Map.
2. map.get() – to retrieve an entry from Map.
3. map.has() – to check existence of an entry in the Map.
4. map.delete() – to delete an entry from the Map.
5. map.size – to return the size of Map.

let nameAgeMapping = new Map();

//1. Add entries
nameAgeMapping.set("Lokesh", 37);
nameAgeMapping.set("Raj", 35);
nameAgeMapping.set("John", 40);

//2. Get entries
nameAgeMapping.get("John");		//40

//Check entry is present or not
nameAgeMapping.has("Lokesh");		//true
nameAgeMapping.has("Brian");		//false

//Size of the Map
nameAgeMapping.size; 				//3

//Delete an entry
nameAgeMapping.delete("Lokesh");	// true

//Clear whole Map
nameAgeMapping.clear();				//Clear all entries

3. Iterating over Map Entries

The Map entries iterate in the insertion order. A for-each loop returns an array of [key, value] pair for each iteration.

Use 'for...of' loop to iterate over map keys, values or entries.

let nameAgeMapping = new Map();

nameAgeMapping.set("Lokesh", 37);
nameAgeMapping.set("Raj", 35);
nameAgeMapping.set("John", 40);

//1. Iterate over map keys
for (let key of nameAgeMapping.keys()) {
    console.log(key);                   //Lokesh Raj John
}

//2. Iterate over map values
for (let value of nameAgeMapping.values()) {
    console.log(value);                 //37 35 40
}

//3. Iterate over map entries
for (let entry of nameAgeMapping.entries()) {
    console.log(entry[0], entry[1]);    //"Lokesh" 37 "Raj" 35 "John" 40
}

//4. Using object destructuring
for (let [key, value] of nameAgeMapping) {
    console.log(key, value);            //"Lokesh" 37 "Raj" 35 "John" 40
} 

Drop me your questions in the comments section.

Happy Learning !!