function abc(){
this.a = "Hey this is A";
}
var va = new abc();
va.prototype = function(){
this.b = 'Hey b is added';
}
console.log(va.b);
va.b is undefined, I thought I already added it to va? since console.log(va) is an object if I console before the prototype line. What's wrong with my code above?
It seems like you really just want to add a property to va:
va.b = "Hey b is added";
If, though, you want to augment the prototype that va already has, you do that through a reference to va's prototype object, which you can get in several ways:
Given your code above, via abc.prototype
Or on ES5+ browsers, via Object.getPrototypeOf(va)
So for instance:
function Abc() {
this.a = "Hey this is A";
}
var va = new Abc();
snippet.log(va.a); // "Hey this is A"
snippet.log(va.b); // undefined
Abc.prototype.b = 'Hey b is added';
snippet.log(va.b); // "Hey b is added"<!-- Script provides the `snippet` object, see http://meta.stackexchange.com/a/242144/134069 -->
<script src="http://tjcrowder.github.io/simple-snippets-console/snippet.js"></script>Note that adding a property to the prototype means that all objects using that prototype will inherit that property:
function Abc() {
this.a = "Hey this is A";
}
var a1 = new Abc();
var a2 = new Abc();
Abc.prototype.b = 'Hey b is added';
snippet.log(a1.b); // "Hey b is added"
snippet.log(a2.b); // "Hey b is added"<!-- Script provides the `snippet` object, see http://meta.stackexchange.com/a/242144/134069 -->
<script src="http://tjcrowder.github.io/simple-snippets-console/snippet.js"></script>
vm, in your question) or the prototype (abc.prototype, in your question).You probably just want to add the property to va.
va.b = 'Hey b is added';
Unless you want a b property added to all instances of abc, then you can add it to abc's prototype:
abc.prototype.b = 'Hey b is added';
va !== abc, instead va instanceof abc
va doesn't point to abc, it does inherit from abc.prototype only.Try this:
<script>
function abc()
{
//constructor
this.a="Hey this is A";
}
abc.prototype.b=function()
{
//prototype
this.b='Hey b is added';
};
var va=new abc();//Initialization
va.b();//value for b is assigned to the context
console.log(va.b);
</script>
Comments are provided..
You didn't create the b property, because you never called va.prototype.
function abc(){
this.a = "Hey this is A";
}
var va = new abc();
va.prototype = function(){
this.b = 'Hey b is added';
};
va.b; // undefined
va.prototype();
va.b; // "Hey b is added"
Note that using prototype as the name for your method can be confusing (there already are the prototype of a function and the [[Prototype]] of an object). I recommend choosing another name.
prototype" as a name for a method.
abc.prototype = ...orva.b = ...va.b = 'Hey b is added';va.prototypeis just a normal property which happens to have the name "prototype". It has nothing to do with prototypal inheritance if that's what you meant.