JavaScript

The Map object in JavaScript offers several methods to manage key-value pairs efficiently. These methods allow you to add, retrieve, delete, and iterate through items.

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📌 1. set(key, value)

Adds a new element with the specified key and value to the Map. If the key already exists, the value will be updated.

✅ Syntax:

map.set(key, value);

🧪 Example:

const map = new Map();
map.set("name", "Alice");
map.set("age", 25);
console.log(map); // Map(2) { "name" => "Alice", "age" => 25 }

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📌 2. get(key)

Returns the value associated with the given key.

✅ Syntax:

map.get(key);

🧪 Example:

console.log(map.get("name")); // Alice

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📌 3. delete(key)

Removes the element associated with the specified key.

✅ Syntax:

map.delete(key);

🧪 Example:

map.delete("age");
console.log(map); // Map(1) { "name" => "Alice" }

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📌 4. has(key)

Checks whether the Map contains a specific key. Returns true or false.

✅ Syntax:

map.has(key);

🧪 Example:

console.log(map.has("name")); // true
console.log(map.has("age"));  // false

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📌 5. clear()

Removes all key-value pairs from the Map.

✅ Syntax:

map.clear();

🧪 Example:

map.clear();
console.log(map); // Map(0) {}

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📌 6. size

Returns the number of key-value pairs in the Map.

✅ Syntax:

map.size;

🧪 Example:

const fruits = new Map([
  ["apple", 10],
  ["banana", 20],
]);
console.log(fruits.size); // 2

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📌 7. forEach(callback)

Calls the provided function once for each key-value pair in the Map.

✅ Syntax:

map.forEach(function(value, key, map) {
  // your logic
});

🧪 Example:

fruits.forEach((value, key) => {
  console.log(`${key} = ${value}`);
});

Output:

apple = 10
banana = 20

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📌 8. [Symbol.iterator]() or entries()

Returns an iterator of [key, value] pairs, making it usable in a for...of loop.

✅ Example:

for (let [key, value] of fruits) {
  console.log(key, value);
}

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📌 9. keys()

Returns an iterator with all the keys in the Map.

✅ Example:

for (let key of fruits.keys()) {
  console.log(key);
}

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📌 10. values()

Returns an iterator with all the values in the Map.

✅ Example:

for (let value of fruits.values()) {
  console.log(value);
}

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📌 11. entries()

Returns an iterator of [key, value] pairs — same as using the default Map iterator.

✅ Example:

for (let entry of fruits.entries()) {
  console.log(entry);
}

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🧾 Summary Table

Method / Property	Description
set(key, value)	Adds or updates a key-value pair
get(key)	Gets the value by key
delete(key)	Removes the key-value pair
has(key)	Checks if a key exists
clear()	Clears all entries
size	Returns total entries in Map
forEach()	Iterates over each entry
keys()	Returns an iterator of all keys
values()	Returns an iterator of all values
entries()	Returns an iterator of key-value pairs
[Symbol.iterator]()	Same as entries() — enables for...of loop