JavaScript

A Map is a collection of key-value pairs, where keys can be of any data type — unlike objects, which only allow strings and symbols as keys.

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✅ Key Features of Maps

• Stores key-value pairs.
• Keys can be any type (e.g., objects, functions, etc.).
• Maintains insertion order.
• Easily iterable using for...of.

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🧱 Creating a Map

You can create a Map using the new Map() constructor:

const myMap = new Map();

You can also initialize it with values:

const myMap = new Map([
  ["name", "John"],
  ["age", 30],
]);

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➕ Adding Key-Value Pairs

Use .set() to add a new pair:

myMap.set("country", "India");
myMap.set("age", 25); // updates the value if key exists

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❓ Getting Values

Use .get() to retrieve a value by its key:

console.log(myMap.get("name")); // John

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🗑️ Deleting & Clearing

✅ delete(key)

myMap.delete("age");

✅ clear()

myMap.clear(); // removes all entries

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🔍 Checking Keys

Use .has() to check if a key exists:

console.log(myMap.has("country")); // true or false

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🧮 Getting Size

Use .size to get the number of entries in the map:

console.log(myMap.size);

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🔁 Looping Through a Map

✅ Using for...of

for (let [key, value] of myMap) {
  console.log(key + " = " + value);
}

✅ Using forEach()

myMap.forEach((value, key) => {
  console.log(key + " => " + value);
});

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🧪 Map with Different Key Types

const map = new Map();

const objKey = { id: 1 };
map.set(objKey, "Object as Key");

map.set(100, "Number as Key");
map.set(true, "Boolean as Key");

console.log(map.get(objKey));  // Object as Key
console.log(map.get(100));     // Number as Key
console.log(map.get(true));    // Boolean as Key

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🧾 Summary of Map Methods

Method / Property	Description
set(key, value)	Adds or updates a key-value pair
get(key)	Returns the value for a given key
delete(key)	Removes a key-value pair
has(key)	Checks if a key exists
clear()	Removes all entries
size	Returns the number of key-value pairs
forEach()	Iterates over map entries

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📘 When to Use Maps?

• You need key-value storage with non-string keys.
• You care about the order of your data.
• You need performance for frequent additions/removals.

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