🚀 JavaScript Map (HashMap) Basics

  • Definition: A Map stores key-value pairs and maintains insertion order.
  • Key Types: Any (string, number, object, etc.).

✅ Common Methods 

const map = new Map();

// Add/Update
map.set('a', 1);

// Get
map.get('a'); // 1

// Check existence
map.has('a'); // true

// Delete
map.delete('a');

// Size
map.size; // 0

// Clear all
map.clear();

🔄 Iterating 

for (const [key, value] of map) console.log(key, value);
map.forEach((value, key) => console.log(key, value));

🆚 Map vs Object

Feature Map Object
Key Types Any String/Symbol
Order Maintains Unordered
Iteration Easy Complex
Performance Better for frequent updates Slower

✅ Use Map when:

  • Keys are not just strings.
  • Frequent add/remove operations.
  • Need to maintain insertion order.

Javascript Code

/**
 * @param {string} ransomNote
 * @param {string} magazine
 * @return {boolean}
 */
var canConstruct = function (ransomNote, magazine) {
    let myMap = new Map();

    for (item of magazine) {
        myMap.set(item, (myMap.get(item) || 0) + 1);
    }
    for (item of ransomNote) {
        const count = myMap.get(item);
        if (!count) return false;
        myMap.set(item, count - 1);
    }

    return true
};