In this article, we will see different approaches to update the value for a specific key in Map in JavaScript. JavaScript Map is a collection of key-value pairs. We have different methods to access a specific key in JavaScript Map.

Methods to update the value for a specific key in Map in JavaScript

Method 1: Using JavaScript Map.set() method

In this method, we will use the built-in Map.set() method to update the value for a specific key.

Example: In this example. we will update the value of key(‘b’) in the given map using the map.set() method.

let m = new Map([
      ["a", 100],
      ["b", 200],
]);

console.log("Old value for key: 'b', "+m.get('b'));
m.set('b',1000)
console.log("New value for key: 'b', "+m.get('b'));

Old value for key: 'b', 200
New value for key: 'b', 1000

Method 2: Using Map.forEach() method

In this method, we will iterate the map using map.forEach() method to iterate the key-value pairs and update the value for specific key.

Example: In this example, we will iterate map using forEach method and update the value for a specific key using if condition.

// Creating a map object
let m = new Map([
    ["a", 100],
    ["b", 200],
]);

// Display old value
console.log("Old value for key: 'b', " + m.get("b"));


// Iterate and change the required value 
m.forEach((value, key) => {
    if (key == "b") m.set(key, 1000);
});

// Display updated value
console.log("New value for key: 'b', " + m.get("b"));

Old value for key: 'b', 200
New value for key: 'b', 1000

Method 3: Using JavaScript Map.has() and Map.set() Methods

In this method, we will first check if the Map contains the specific key using the has() method. If the key is present, we will then use the set() method to update its value.

Example:

// Creating a map object 
let m = new Map([ 
    ["a", 100], 
    ["b", 200], 
]); 

// Display old value 
console.log("Old value for key: 'b', " + m.get("b")); 

// Check if the key exists and update the value
if (m.has("b")) {
    m.set("b", 1000);
}

// Display updated value 
console.log("New value for key: 'b', " + m.get("b")); 

Old value for key: 'b', 200
New value for key: 'b', 1000

In this example, we will update the value of key (‘b’) in the given map only if it exists, using the has() and set() methods.