Object.assign in javascipt

    
    Object.assign is used for merging object & cloning purpose.

    Merging Objects in JavaScript


        var o1 = { a: 1 };
        var o2 = { b: 2,a:5 };
        var o3 = { c: 3 };

       var obj = Object.assign(o1, o2, o3);

        console.log(obj); // { a: 5, b: 2, c: 3 }
        console.log(o1);  // { a: 5, b: 2, c: 3 }, target object itself is changed.
        console.log(o2); // {b: 2,a:5 }
        console.log(o3); // { c: 3 }

    Here we are merging o1,o2,o3 object during merge o1 also get merged object value along with returned object "obj". 'a' happens to be in o1 & o2 so in merged object a get value from last object  with a defined in it based on sequence in which they comes in Object.assign.

        Copying Object
              Though object.assign copies object deep clone is not happening.

        var obj2 = Object.assign({ p: 67 }, { q: 09 }, { r: 34 });
        console.log(obj2);

        let obj3 = {person: 'Thor Odinson',adr:{city:"mumbai"}};
        let clone = Object.assign({}, obj3);

        obj3.person ="test"
        obj3.adr.city="kolkota"

        console.log(clone);
        console.log(obj3);


         obj3 adr-->city in copied to "clone" by reference unlike key "person".so deep coping is not happening ,change in source adr-->city will modify in cloned object also.

        Deep Clone:
        let obj4 = {person: 'Thor Odinson',adr:{city:"mumbai"}};
        let deep_clone = JSON.parse(JSON.stringify(obj4))

        obj4.adr.city="pune"
        console.log(deep_clone);
        console.log(obj4);


    Deep clone is possible using JSON.parse(JSON.stringify()) call on object.

 Shallow Copy Example:

var employeeDetailsOriginal = {  name: 'Manjula', age: 25, Profession: 'Software Engineer' };
var employeeDetailsDuplicate = employeeDetailsOriginal; //Shallow copy!
employeeDetailsDuplicate.name = 'NameChanged';

console.log(employeeDetailsOriginal);

console.log(employeeDetailsDuplicate);

Output:
{ name: 'NameChanged', age: 25, Profession: 'Software Engineer' }
{ name: 'NameChanged', age: 25, Profession: 'Software Engineer' }

     Ellipses in Javascript:


           var obj33 =[{a:4,b:7},{p:6,q:5}]
           var obj5 = [... obj33];
           obj33[0].a =44
           console.log(obj5);
           console.log(obj33);


     object array copied using ellipses syntax also not deep clone.

   Copying property by looping:

    var person = {
            name: 'John',
            age: 28,
            adr:{state:"maha"}
    };

    var newPerson = new Object();
    for(prop in person){
      newPerson[prop] = person[prop];
    }

    newPerson.adr.state="karnataka"
    newPerson.age = 30
    console.log(newPerson === person)
    console.log(person)
 
   copying property by looping in object also do not deep clone.