CODEWITHSUNDEEP
javascriptprototype
user3144851
user3144851

Reputation: 39

Accessing object properties with prototype

I know there are several ways to create Objects, add Methods and Properties etc. There is one thing I don't understand about prototypes

  function Obj () {
    var msg = "message";

    this.log = function (){
      console.log(msg);
    }
  }
  var o = new Obj();
  o.log();

this would output message. however using a prototype

function Obj2 () {
  var msg = "message2";

}

Obj2.prototype.log = function () {
  console.log(msg);
}

var o2 = new Obj2();
o2.log();

would output that msg is not defined. why is that?

Upvotes: 0

Views: 36

Answers (2)

V31
V31

Reputation: 7666

You have a scope problem as mentioned by @Quentin, However if you need to access the variable inside the prototype function, you need to make use of this and treat it as a class. So now it will be treated as a property to the class Obj2 and not as a private variable.

So the code will be like:

function Obj2 () {
  this.msg = "message2";

}

Obj2.prototype.log = function () {
  console.log(this.msg);
}

var o2 = new Obj2();
o2.log();

Fiddle Demonstration

Upvotes: 0

Quentin
Quentin

Reputation: 944568

msg is a variable that is scoped to Obj and Obj2 respectively.

The log function in the first example is defined within the scope of Obj so it has access to variables from that scope.

The log function in the second example is not defined within that scope of Obj2, so it doesn't.

Upvotes: 1

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