Map - JavaScript

Map

Description :

Map objects are collections of key-value pairs. A key in the map may only occur once. It is unique in the Map's collections. A Map object is iterated by key-value pairs through for--of loop return 2 member array of [key, value] for each iteration. Iteration happens in insertion order, which corresponds to the order in which each key-value pair was inserted into the map by the set() method.

Property of Map:

1. The first property of the Map is its size.

   The size accessor property returns the number of elements in a Map object.

   
    const map1 = new Map();
   
    map1.set('a', 'alpha');
    map1.set('b', 'beta');
    map1.set('g', 'gamma');
    map1.set('shushil',{phone:"393975782", address:"123 N 1st Ave"})
   
    console.log(map1.size);// Expected output: 4
    console,log(map1.get('a'); // Output : alpha
   

   Map() constructor

   The Map() constructor creates Map objects.

   Syntax

   new Map()

   new Map(Iterable)

   Creating a new Map

    //New Map (iterable) or parameters
    const myMap=new Map([[1,'one'],[2,'two'],[3,'three']])
    // new Map
    const myMap=new Map();
   

   Instance Methods

   1. The clear() method is used to remove all elements from a Map object.

   Demo:

    // Clear()
    const map1 = new Map();
    map1.set('name', "Sushil")
    map1.set('surname', "chuabey");
   
    console.log(map1.size);  // Output: 2
   
    map1.clear();
   
    console.log(map1.size) // Output: 0
   

   2. The delete() method is used to remove the specified element from a Map object by key.

   Demo:

    const map1 = new Map();
    map1.set('name', "Sushil")
    map1.set('surname', "chuabey");
   
    console.log(map1.size); // Output:2
   
    console.log(map1.delete('name')); // delete "name" 
    console.log(map1); // Output : 'surname', 'chuabey'
   

   3. The has() method returns a boolean indicating whether an element with the specified key exits or not.

   Demo:

    const map1 = new Map();
    map1.set('name', "Sushil")
    map1.set('surname', "chuabey");
   
    console.log(map1.size);
    console.log(map1.has('name'); // output: True;
   

   4. The keys() method returns a new iterator object that contains the keys for each element in the Map object in insertion order.

   Demo:

    const map1 = new Map();
   
    map1.set('0', 'foo');
    map1.set(1, 'bar');
   
    const iterator1 = map1.keys();
    console.log(iterator1); //  Expected output: {0,1)}
   
    console.log(iterator1.next().value); 
    // Expected output: "0"
   
    console.log(iterator1.next().value);
    // Expected output: 1
   

   5. The values() the method returns a new iterator object that contains the values for each element in the Map object in insertion order.

   Demo:

    const map1=new Map()
    map1.set('0', 'shusil');
    map1.set(1, 'chaubey');
   
    const iterator1 = map1.values();
    console.log(iterator1); 
     // Output: {"shusil", "chaubey"}
   
    console.log(iterator1.next().value);
    // Expected output: "shusil"
   
    console.log(iterator1.next().value);
    // Expected output: "chaubey"
   

   6. The entries()method returns a new iterator object that contains the [key, value] pairs for each element in the Map object in insertion order.

   Demo:

    const map1 = new Map();
   
    map1.set('0', 'shushil');
    map1.set(1, 'chaubey');
   
    const iterator1 = map1.entries();
    console.log(iterator1); 
    // Expected output : Array {["0", "shushil"],[1,"chaubey"]}
   
    console.log(iterator1.next().value);
    // Expected output: Array ["0", "shushil"]
   
    console.log(iterator1.next().value);
    // Expected output: Array [1, "chaubey"]