JavaScript Objects

Objects in JavaScript are used to store keyed collection of various data and more complex entities.

An object can be created with {..} with an optional list of properties. A property is a “key: value” pair, where key is a string(also called as property name) and value can be anything.

An empty object can be created using one of the two methods

let user=new Object();   //object constructor syntax
let user={};            // object literal syntax

We can immediately put some properties into {...} as “key: value” pairs:

let user={
 name:"vinod",
 age:30
};

A property has a key (also known as “name” or “identifier”) before the colon ":" and a value to the right of it.

In the user object, there are two properties:

1. The first property has the name "name" and the value "vinod".
2. The second one has the name "age" and the value 30.

Property values are accessible using the dot notation:

// get property values of the object:
alert( user.name ); // vinod
alert( user.age ); // 30

The value can be of any type. Let’s add a boolean one:

user.isAdmin = true;

To remove a property, we can use the delete operator:

delete user.age;

We can also use multiword property names, but then they must be quoted:

let user = {
  name: "vinod",
  age: 30,
  "likes birds": true  // multiword property name must be quoted
};

For multiword properties, the dot access doesn’t work:

// this would give a syntax error
user.likes birds = true

JavaScript doesn’t understand that. It thinks that we address user.likes, and then gives a syntax error when comes across unexpected birds.

The dot requires the key to be a valid variable identifier. That implies: contains no spaces, doesn’t start with a digit and doesn’t include special characters ($ and _ are allowed).

There’s an alternative “square bracket notation” that works with any string:

let user = {};

// set
user["likes birds"] = true;

// get
alert(user["likes birds"]); // true

// delete
delete user["likes birds"];

Source: javascript.info