TypeScript Map

TypeScript Map is a built-in data structure that allows you to store key-value pairs and remembers the original insertion order of the keys similar to other programming languages where keys and values can be of any data type.

Syntax:

let myMap = new Map<KeyType, ValueType>();

Parameters:

• KeyType: The data type of the keys in the map.
• ValueType: The data type of the values associated with the keys in the map.

Common Methods and Properties:

• set(key: KeyType, value: ValueType): Map<KeyType, ValueType>
  • Adds or updates a key-value pair in the map.
  • Returns the updated map.
• get(key: KeyType): ValueType | undefined
  • Retrieves the value associated with the specified key.
  • Returns undefined if the key is not found.
• has(key: KeyType): boolean
  • Checks if the map contains the specified key.
  • Returns true if the key is found; otherwise, false.
• delete(key: KeyType): boolean
  • Removes the key-value pair associated with the specified key.
  • Returns true if the key was found and removed; otherwise, false.
• clear(): void
  • Removes all key-value pairs from the map.
• forEach(callbackfn: (value: ValueType, key: KeyType, map: Map<KeyType, ValueType>) => void, thisArg?: any): void
  • Calls a provided function once for each key-value pair in the map, in insertion order.
• size: number
  • Returns the number of key-value pairs in the map.

Iterating Map Data

Iterating over the key-value pairs in a TypeScript Map can be done using various methods. The forEach the method is commonly used for this purpose.

Example 1: In this example, we are using the forEach method to Iterate over map data:

Javascript

let myMap = new Map<string, number>();

myMap.set("one", 1);
myMap.set("two", 2);
myMap.set("three", 3);

// Using forEach method
myMap.forEach((value, key) => {
      console.log(`Key: ${key}, Value: ${value}`);
});

Output:

Key: one, Value: 1
Key: two, Value: 2
Key: three, Value: 3

Example 2: In this example, KeyType is string, and ValueType is number. The methods demonstrate common operations on a TypeScript Map.

Javascript

let myMap = new Map < string, number> ();

myMap.set("one", 1);
myMap.set("two", 2);

console.log(myMap.get("one")); // Output: 1
console.log(myMap.has("two")); // Output: true

myMap.delete("two");
console.log(myMap.size); // Output: 1

myMap.forEach((value, key) => {
    console.log(`Key: ${key}, Value: ${value}`);
});

Output:

1
true
1
Key: one, Value: 1