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How to use "map" object in TypeScript



What is Map in TypeScript?

The Map is a built-in object in TypeScript that is used to store key-value pairs. It's similar to an object in JavaScript, but the keys in a Map can be of any type, including functions, objects, and symbols, whereas object keys can only be strings or symbols.


A Map object is created using the new Map() constructor, and you can add key-value pairs to the Map using the set() method. To retrieve a value from the Map, you use the get() method, passing in the key as an argument. To check if a key exists in the Map, you use the has() method. And to delete a key-value pair from the Map, you use the delete() method.


Steps to use the "map" object

Here are the steps to use a Map object in TypeScript:


STEP 1: Create a new Map object:

const map = new Map<KeyType, ValueType>();

Replace KeyType and ValueType with the desired types for the keys and values in the Map.


STEP 2: Add key-value pairs to the Map:

map.set(key, value);

Replace the key and value with the actual key and value to be added to the Map.


STEP 3: Retrieve a value from the Map using its key:

const value = map.get(key);

Replace the key with the actual key of the value to be retrieved.


STEP 4: Check if a key exists in the Map:

const exists = map.has(key);

Replace the key with the actual key to be checked.


STEP 5: Remove a key-value pair from the Map:

map.delete(key);

Replace the key with the actual key of the key-value pair to be removed.


STEP 6: Iterate over the Map object:

for (const [key, value] of map) 
{
  // Your code here
}

In each iteration, the current key and value are destructured from the Map entry as key and value.


Example:

const map = new Map<string, number>();  

map.set("key1", 1); 
map.set("key2", 2); 
map.set("key3", 3);  

console.log(map.get("key1")); // Output: 1 
console.log(map.get("key2")); // Output: 2 
console.log(map.get("key3")); // Output: 3  

console.log(map.has("key1")); // Output: true 
console.log(map.has("key4")); // Output: false

map.delete("key2"); 
console.log(map.has("key2")); // Output: false

for (const [key, value] of map) 
{   
    console.log(`${key}: ${value}`); 
}

Output:

key1: 1
key3: 3

We create a Map object with string keys and number values in this example. We then add three key-value pairs to the Map using the set method. We retrieve the values using the get method, check if keys exist using the has method remove a key-value pair using the delete method, and finally, iterate over the Map using a for-of loop.


TypeScript Map Methods

Here are some common methods of the Map object in TypeScript, along with a detailed explanation of each:


Method 1: set(key: KeyType, value: ValueType)

Adds a new key-value pair to the Map object. The key argument specifies the key, and the value argument specifies the value. If the specified key already exists in the Map, the associated value is updated with the new value.

let map = new Map<string, number>();
map.set("key1", 1);
map.set("key2", 2);
console.log(map); // Map { 'key1' => 1, 'key2' => 2 }

Method 2: get(key: KeyType)

Retrieves the value associated with the specified key from the Map object. If the key does not exist, undefined is returned.

let map = new Map<string, number>();
map.set("key1", 1);
console.log(map.get("key1")); // 1
console.log(map.get("key2")); // undefined

Method 3: has(key: KeyType)

Returns true if the specified key exists in the Map object, and false otherwise.

let map = new Map<string, number>();
map.set("key1", 1);
console.log(map.has("key1")); // true
console.log(map.has("key2")); // false

Method 4: delete(key: KeyType)

Removes the key-value pair associated with the specified key from the Map object.

let map = new Map<string, number>();
map.set("key1", 1);
map.delete("key1");
console.log(map); // Map {}

Method 5: clear()

Removes all key-value pairs from the Map object.

let map = new Map<string, number>();
map.set("key1", 1);
map.set("key2", 2);
map.clear();
console.log(map); // Map {}

Method 6: keys()

Returns an iterable object of all the keys in the Map object.

let map = new Map<string, number>();
map.set("key1", 1);
map.set("key2", 2);
for (let key of map.keys()) {
  console.log(key);
}
// Output:// key1// key2

Method 7: values()

Returns an iterable object of all the values in the Map object.

let map = new Map<string, number>();
map.set("key1", 1);
map.set("key2", 2);
for (let value of map.values()) {
  console.log(value);
}
// Output:// 1// 2

Method 8: entries()

Returns an iterable object of all the key-value pairs in the Map object.

let map = new Map<string, number>();
map.set("

Frequently Asked Questions

Here are some common FAQs regarding Map objects in JavaScript:


Question 1: What is a Map object in TypeScript?

Answer: The Map is a built-in object in TypeScript that is used to store key-value pairs, similar to an object. However, unlike objects, the keys in a Map can be of any type, including functions, objects, and symbols.


Question 2: How do I create a Map object in TypeScript?

Answer: You can create a Map object using the new Map<KeyType, ValueType>() constructor, where KeyType and ValueType are the types of the keys and values in the Map.


Question 3 How do I add items to a Map object in TypeScript?

Answer: You can add items to a Map object using the set method, passing in the key and the value as arguments.


Question 4: How do I retrieve an item from a Map object in TypeScript?

Answer: You can retrieve an item from a Map object using the get method, passing in the key as an argument.


Question 5: How do I check if a key exists in a Map object in TypeScript?

Answer: You can use the has method to check if a key exists in a Map object, passing in the key as an argument.


Question 6: How do I remove an item from a Map object in TypeScript?

Answer: You can remove an item from a Map object using the delete method, passing in the key as an argument.


Question 7: How do I iterate over a Map object in TypeScript?

Answer: You can use a forEach loop or a for-of loop to iterate over a Map object in TypeScript.


Question 8: Is a Map object ordered in TypeScript?

Answer: Yes, the items in a Map object are ordered based on the order in which they were inserted.


Question 9: Can I use a Map object with generics in TypeScript?

Answer: Yes, you can use generics with Map objects in TypeScript to specify the types of the keys and values.

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