JavaScript object concepts

4 years ago

Wanna Learn React.js - How To Learn React Quickly

Today, new languages are being created to build a new level of applications that have advanced features and also meet demanding needs of businesses and users.

New programming languages don’t always bring forward big changes. There are many powerful languages that always are around. Among them JavaScript that is always in the list of popular programming languages and developers and industry leads are falling in love with it all the time using it everywhere on the web, mobile, server and even on IoT. 

Following are the tricks of object in javascript. These are very important for interview.

1.Length of an object

var arr = [1,2,3,4]

var obj = { a:1, b:2 };

var length = Object.keys(obj).length;

console.log(obj.lengt);  // undefined

console.log(length) ; // 2

2.Iterating over an object

 var username = {

  firstName: "aman",



//First approach

for(let u in username){





/* outcome will be

  firstName aman

  lastName tiwari*/

//Second approach

for(let u in Object.keys(username)){

 console.log(u, username[u]);


/*outcome will be

 firstName aman

 lastName tiwari*/

//Third approach

Object.entries(username).forEach(([key,value]) => console.log(key, value));

/*outcome will be

 firstName aman

 lastName tiwari*/

3.Object to array conversion

var person = { name: "aman", age:"20"}

   var arr =[];

   //First approach

   Object.keys(person).forEach(key => arr.push([key, person[key]]));

   console.log(arr) // [['name', 'aman'], ['age', 20]]

   //Second approach

   var result = Object.keys(person).map(key => [key, person[key]])

  console.log(result) // [['name', 'aman'], ['age', 20]]

  //third approach

  console.log(Object.entries(person));// [['name', 'aman'], ['age', 20]]

4.Check if property exist in object

var user = {

 name: "aman",

 address: {

  street: "Hauz khas Enclave",

  city: "New Delhi"



var property = 'name' in user;

console.log(property) //true

5.Merge multiple object into one object

 var defaultUser = {





var actualUser = {

 name: "Aman",

 email:"[email protected]"


var userData = Object.assign(defaultUser, actualUser);

console.log(userData);  // { name: "Aman", email:"[email protected]", subscribe:true}

6.Filter property of object

  var filterObj ={}

  var name = { name: 'aman' , age: "20"}

 const result = Object.keys(name)

                 .filter(key => key !=='name')

                 .map(key => filterObj[key]=name[key]);

  console.log(filterObj) //{ age: 20 }

7.Get all values in object

var name = {

 firstName: "aman",


 age: "20",


var values = Object.keys(name).map(key => name[key]);

console.log(values); // ['aman', 'tiwari', '40']

P.S - reach out to me incase you have doubts

Happy coding