object-methods.md

Object and It's Methods in JavaScript

How to create object in JavaScript?

// simple and most popular way to create object
const person = {
    name: 'Deepa'
};

You can also use new keyword

const person1 = new Object();
person1.name = 'Deepa';
console.log(person1); // {name: 'Deepa'}

You can also use 'new' with user defined constructor function.
E.g.

function person(name) {
    this.name = name;
}
// Now anytime you want person object.
const personOne = new person('deepa');
const personTwo = new person('partha');
console.log(personOne); // {name: 'deepa'}
console.log(personTwo); // {name: 'partha'}

Using Object.create() to create new Objects

The Object.create() methods creates a new object, using an existing object as prototype of the newly created object.

It contains two parameter:

• First parameter is mandatory that serves prototype of new object to be created.
• Second is optional, it contains properties to be added to new object.
  

E.g.

const orgObject = { company: 'ABC' };
const employee = Object.create(orgObject, { name: { value: 'EmpOne'}});
console.log(employee); // {name: 'EmpOne'}
console.log(employee.name); // EmpOne

Using Object.assign() to create new object

The Obeject.assign() method is used to copy all enumerable own properties value from one or more source objects to target object. It will return target object.

E.g.

const orgObject = { company: 'ABC' };
const carObject = { carName: 'Corola' };
const employee = Object.assign({}, orgObject, carObject);

// Now you can get employee object that has company and carName as its property.

console.log(employee); // {company: 'ABC', carName: 'Corola'}

Using Object.defineProperties()

This method defines new or modify existing property on object.

const object1 = {};
Object.defineProperties (object1, {
    property1: {
        value: 42
    }
});
console.log(object1.property1); // 42

Similarly, we also have Object.defineProperty()

Using Object.Entries()

It returns an array of object's key value pairs.
The order of array is same as provided by a for in loop

const object1 = {
    a: 'something', 
    b: 'nothing'
};
for (const [key, value] of Object.entries(object1)) {
    console.log(`${key}: ${value}`);
}
/* Output:
    a: something
    b: nothing
*/

Object.freeze()

It freezes an object. No longes can be changed.
E.g.

const obj = {
    prop: 42
};
Object.freeze(obj);
obj.prop = 43;
console.log(obj.prop); // 42
// It can no longes be change due to freeze

Object.fromEntries()

It transforms a list of key-value pairs into an object.
E.g.

const entries = new Map([
    [ 'foo', 'bar' ],
    [ 'baz', 42 ]
]);
const obj = Object.fromEntries(entries);
console.log(obj); // {foo: 'bar', baz: 42}