JavaScript Objects

An object is an excellent data structure in JavaScript. Why it’s awesome? Because it stores data as a key and value as a pair; apart from that every key is unique so we can store unique information inside objects. Now let’s understand, How to implement this data structure, the syntax for an object is –

How to create an object

var obj = {}; // An Empty object

// Or

var obj = new Object();

The basic structure of an object like the below code –

var variabl_name = { 'key_1': value };

var obj = { 'name': 'xyz', 'age': 23 };

How to access the property

Here we have to way to access the property of an object

obj.propertyname // using dot
obj[propertyname] // using bracket 

/* Like - */ // "xyz"
obj["name"] //name

We can not use the dot operator if our key is separated by a hyphen.

obj["stu-name"] = "John" 

// Can't use like

obj.stu-name; // Error

How to delete property

To delete a property we can use the delete keyword


How to get the length of a javascript object

We will use keys properly

var obj = { name: "xyz", age: 23 };

console.log(Object.keys(obj), " and length will be ", Object.keys(obj).length);

// ["name", "age"] and length will be 2

Object tricks

A lot of time we want to access or set dynamic key and we don’t know about that key so how we can access that property?

let key = prompt("what information you want to know about user?", "name");
console.log(obj[key]); // xyz

Instead of name: name we can write a name, like this:

function dummyObj(name, age) {
  return {
    name: name,
    age: age
    // ...other properties

var obj = makeUser("xyz", 30);
console.log(; // xyz

Power of in keyword

Supposed that you have a condition and you want to check key is part of an object like this example –

var obj = {
val: undefined

console.log(obj.test); // undefined
console.log("val" in obj); // true

Access all keys with for in loop

We have for keyword to access all key but with the help of in it become easier to use –

for (var o in obj) {
     console.log(key, o[key]); 
     //name xyz
     // age 23

About the Author: Pankaj Bisht