TypeScript Map

TypeScript Map is a new data structure introduced in ES6. A Map allows storing key-value pairs (i.e. entries), similar to the maps in other programming languages e.g. Java HashMap.

1. Creating a Map

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

let myMap = new Map();

To create a Map with initial key-value pairs, pass the key-value pairs 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 available in a Map are:

• map.set(key, value) – adds a new entry in the Map.
• map.get(key) – retrieves the value for a given key from the Map.
• map.has(key) – checks if a key is present in the Map.
• map.delete(key) – deletes a key-value pair using its key.
• map.clear() – deletes all entries from the Map.
• map.size – returns the count of entries in the 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

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

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

• map.keys() – to iterate over map keys
• map.values() – to iterate over map values
• map.entries() – to iterate over map entries
• map – to iterate over map 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
}

Happy Learning !!