A Map is a built-in JavaScript object that holds key-value pairs, maintaining the order of insertion. Unlike objects, keys in maps can be any data type including functions, objects, and primitives.

const map = new Map();

Using the Constructor

const map = new Map([
  ['key1', 'value1'],
  ['key2', 'value2']
]);

This creates a new map with two entries.

• set(key, value) – Adds or updates an entry.
• get(key) – Retrieves the value by key.
• has(key) – Returns true if the key exists.
• delete(key) – Removes the key and value.
• clear() – Removes all entries.
• size – Returns the number of entries.

map.set('a', 1);
console.log(map.get('a'));  // 1
console.log(map.has('a'));  // true
map.delete('a');

Methods for Iteration

• map.keys() – Returns an iterator over keys.
• map.values() – Iterator over values.
• map.entries() – Iterator over key-value pairs.
• map.forEach(callback) – Executes callback for each entry.

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

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

Feature	Map	Object
Key types	Any (including objects)	Strings & Symbols only
Order	Preserved	Not guaranteed
Performance	Better for frequent additions/removals	Better for static structure

• Storing user sessions or caches where keys are objects
• Implementing lookup tables
• Preserving key insertion order
• Using methods like forEach without side-effects from prototypes