Introduction to Maps in JavaScript

In JavaScript, maps are a data structure that allow you to store key-value pairs where both keys and values can be of any data type. Maps are similar to objects, but they have some differences and additional functionalities.

Basic Usage:

  1. Creating a Map:

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

                        // Creating a new map
                        let myMap = new Map();                    

  2. Adding Entries:

    To add key-value pairs to a map, you can use the set() method:

                        // Adding entries to the map
                        myMap.set('key1', 'value1');
                        myMap.set(2, 'value2');
                        myMap.set({ key: 'key3' }, 'value3');                    

  3. Getting Values:

    You can retrieve values using the get() method, passing in the key:

                        // Retrieving values from the map
                        console.log(myMap.get('key1')); // Output: value1
                        console.log(myMap.get(2)); // Output: value2                    

  4. Checking Size:

    To know the number of entries in a map, use the size property:

                        // Checking the size of the map
                        console.log(myMap.size); // Output: 3                   

  5. Iterating through a Map:

    You can iterate through a map using various methods like forEach(), for...of, or the entries() method:

                        // Iterating through the map
                        myMap.forEach((value, key) => {
                          console.log(`${key} => ${value}`);
                        // Using for...of loop
                        for (let [key, value] of myMap) {
                          console.log(`${key} => ${value}`);

Key Differences from Objects:
  • Key Types: In objects, keys are always converted to strings. In maps, keys can be of any data type (objects, functions, primitives, etc.).
  • Order Preservation: Maps maintain the order of keys. This can be useful when iterating through them as they maintain insertion order.
  • Size Property: Maps have a size property that provides the number of key-value pairs.


Maps have various methods for managing and retrieving data, such as set(), get(), has(), delete(), clear(), forEach(), keys(), values(), and entries().


            let myMap = new Map();

            myMap.set('name', 'Alice');
            myMap.set('age', 30);
            myMap.set('dob', '1990-01-01');
            console.log(myMap.get('name')); // Output: Alice
            console.log(myMap.has('age')); // Output: true
            myMap.forEach((value, key) => {
              console.log(`${key} => ${value}`);

Maps are versatile and useful for various scenarios where you need to store key-value pairs and maintain their order. They're handy for situations where you need more flexibility than what objects offer.

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