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01history
02introduction
03javascript runtime environment
04token
05scope
06global execution context
07var let const
08function
09practice questions
10lexical scope
11closure
12interview questions
13array
14object
15json
16call apply bind
17constructor function
18this keyword
19destructuring
20rest and spread
21string
22prototype
23dom
24event
25exception handling
26asynchronous javascript
27non promise based apis
28what is promise
29frequently asked questions

#object

  1. 1. An Object is a block of memory which has state(variable) , behaviour(methods) and where we can store heterogenous data.
  2. 2. An object is a collection of key-value pairs that can contain various data types, such as numbers, strings, arrays, functions, and other objects.
  3. 3. In one object we can have multiple key value pair and it should be separated by ',' comma.
  4. 4. We can access value of object using (.) Operator or square bracket [] , object reference and key_name.

#object Key (property)

  1. 1. Object key (property) will be automatically converted into string by js engine.
  2. 2. If keys name are in Number , js engine will convert them into string and arrange them in ascending order.
  3. 3. To write space separated key names , we have to enclose key name with double quotes.
  4. 4. If we want to give computed or user defined property then we have to use square brackets and variable name.
  5. 5.

    If key-name is same as variable name which hold the value , instead of writing two times we can write varaiable name only once.

    1let phone = 8800425635;
    2let obj = {
    3  phone,
    4  // phone:phone
    5};

#Ways to create Object

  1. 1.

    By using curly braces { } and literals.

    1let obj = {}
    2// empty object
    3
    4let obj = { name:"chombi",age:16}
    5// object with literals
  2. 2.

    By using new keyword and Constructor.

    1let obj = new Object();
    2// {} empty object
    3
    4let obj=new Object({ name:"chombi"});
    5// { name:"chombi"} object with literals
  3. 3. By using new keyword and Constructor function
  4. 4. By using class

#Access object value

  1. 1.

    By using dot operator ( . ) and key name.

    1let obj = { name:"chombi",age:16}
    2
    3console.log(obj.name)// chombi
    4console.log(obj.age)// 16
  2. 2.

    By using square brackets ( [] ) and key name.

    1let obj = { name:"chombi",age:16}
    2
    3console.log(obj["name"])// chombi
    4console.log(obj["age"])// 16
  3. 3. If we try to access property which is not available in object we will get undefined.

#Object Methods

  1. 1. In JavaScript, object methods are functions that are attached to the object, and can be called on that object reference.
  2. 2. To call a function , we use square brackets instead dot operator.
  3. 3.

    Here, speak is a variable which holds the function reference.

    1let obj1 = { name: "chombi",
    2age: 16,
    3speak: function () {
    4console.log('i can speak');
    5} }
    6console.log(obj1["speak"]());
    7//i can speak
  4. 4.

    Access object property inside function - function declared with function keyword.

    1let obj1 = { name: "chombi",
    2age: 16,
    3speak: function () {
    4console.log('My name is' + this.name+',age' + this.age+' and i can speak');
    5} }
    6console.log(obj1["speak"]());
    7//My name is chombi , age 16 and i can speak

    Here, we can access object property, by using 'this' keyword.
  5. 5.

    Access object property inside function - Arrow function.

    1let obj1 = {
    2  name: "chombi",
    3  age: 16,
    4  speak: () => {
    5    console.log(
    6      "My name is" + obj1.name + " , age " + obj1.age + " and i can speak"
    7    );
    8  },
    9};
    10console.log(obj1["speak"]());
    11//My name is chombi , age 16 and i can speak
    12// Here, we can access object property, by using object reference.

    Here , we can can access object property , by using object reference because arrow function is not having 'this' property.

#Add key value in object

  1. 1. To add key-value pair we can using dot operator and square brackets
  2. 2.

    By using dot operator ( . ) and key name

    1let obj = { name:"chombi",age:16}
    2
    3obj.country = "india";
    4//new key-value added in object
    5// {
    6name:"chombi",
    7age:16,
    8country:"india",
    9}

    NOTE : If property is already available with same name it will updated with new value.
    Example:
    let obj = { name:"chombi",age:16 }
    obj.age = 18;
    //age property value is updated
    // {
    name:"chombi",
    age:18,
    }

#Check property is available in Object or not

  1. 1.

    We can check using "in" operator.

    Syntax : "property name" in object_name

    1let obj = { name:"chombi",age:16}
    2
    3obj.country = "india";
    4//new key-value added in object
    5// {
    6name:"chombi",
    7age:16,
    8country:"india",
    9}


    We can check using "in" operator.

    1let obj = { name:"chombi",age:16}
    2
    3console.log("name" in obj )// true
    4console.log("age" in obj )// true
    5console.log("city" in obj )// false

#Copy of object

  1. 1. We can create copy of two types :

    • 1. Shallow copy
    • 2. Deep Copy

  2. 2. Shallow copy

    • 1. The copy of object that is directly connected with original object is called as shallow object.
    • 2. Here, we store reference of original object in a new varaiable , now new variable starts pointing to same memory block.
    • 3. So if we make any changes in copy , it will be reflected to original object because both variables are pointing to same memory block.
    • 4. 
      1let obj = { name:"chombi",age:16}
      2
      3let obj_cpy = obj;
      4//reference of obj is copied in obj_cpy
      5
      6obj_copy.age=20;
      7console.log(obj_copy);
      8//{ name:"chombi",age:20 }
      9console.log(obj);
      10//{ name:"chombi",age:20 }

  3. 3. Deep copy

    • 1. The copy in which original object is not connected with it's copy , is called as Deep copy.
    • 2. Here , we create separate empty object and after that we copy key-value pair of original object into new empty object.
    • 3. Now , if we make any changes in copy , it will not be reflected to original object because we have create separate memory blocks.
    • 4.

      Create copy using for loop.

      1let obj1 = {name:"chombi",age:16}
      2
      3let obj2 = { }
      4// new empty object
      5
      6
      7for (prop in obj1) {
      8obj2[prop] = obj1[prop]
      9console.log(obj2)
      10}
      11//copy key-values into new object
      12
      13obj2.age=20;
      14console.log(obj2);
      15//{ name:"chombi",age:20 }
      16console.log(obj1);
      17//{ name:"chombi",age:16 }

#Object in-built Methods

  1. 1. Object.keys(obj_ref)

    • 1. Returns an array of given object's property names.
    • 2. 
      1const obj = { a: 1, b: 2, c: 3 };
      2console.log(Object.keys(obj));
      3// Output: ["a", "b", "c"]

  2. 2. Object.values(obj_ref)

    • 1. Returns an array of given object's values.
    • 2. 
      1const obj = { a: 1, b: 2, c: 3 };
      2console.log(Object.values(obj));
      3// Output: [1,2,3]

  3. 3. Object.entries(obj_ref)

    • 1. Returns an array of key-value pairs in an array.
    • 2. 
      1const obj = { a: 1, b: 2, c: 3 };
      2console.log(Object.entries(obj));
      3// Output: [[a,1],[b,2],[c,3]]

  4. 4. Object.assign(target_obj,src1,...,srcn)

    • 1. Copies key-value pair from one or more source objects to a target object.
    • 2. 
      1const target = { a: 1, b: 2 };
      2const source = { c: 4, d: 5 };
      3const result = Object.assign(target, source);
      4console.log(result);
      5// Output: { a: 1, b: 2, c: 4, d: 5 }

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