Why does this code run in javascript ? Function inside an object [duplicate]

Question

When i type this code in javascript console, this does not through an error, instead it runs.

var a = { 
  b:"123",
  update(){
     console.log("hello");
  }
}

The problem is, update() does not have a function keyword and when i check the properties of object a , i get :

b: "123"
update: function ()
__proto__: Object

What is javascript actually doing here?

Answer 1

In ECMA Script 6, you can define properties of an Object during its creation, without the :.

For example,

var data = 100;
var a = { data };
console.log(a);
// { data: 100 }

Similarly, in your case, you are creating two properties, one is called b and another one is called update, where b is 100 and update is actually a function object called update.

Read more about it here

---

Note: This is just the shorthand notation introduced in ECMA Script 6. You can still use the ECMA Script 5 way of creating properties which are functions, like this

var a = {
  b: "123",
  update: function update() {
     console.log("hello");
  }
}

Answer 2

The syntax to create a javascript object is :

var person = {
    firstName: "John",
    lastName : "Doe",
    id       : 5566,
    fullName : function() {
       return this.firstName + " " + this.lastName;
    }
};

Here fullnme is a method of the object and can be accessed using:-

person.fullname()

Because of () in your code

var a = { 
  b:"123",
  update(){
     console.log("hello");
  }
}

Javascript is understanding it as a function . Hope this explanation helps.