How to call object's method from constructor?

Question

var Dog = function(name) { this.name = name; this.sayName(); }

Dog.prototype.sayName = function() {
  alert(this.name);
}

I'm creating new instance of Dog object Dog('Bowwow'), but method sayName() is undefined. Why?

Or maybe I should do something like (but I can't see difference)...

var Dog = function(name) {

  this.name = name;

  this.sayName();

  this.prototype.sayName = function() {
    alert(this.name);
  }
}

Thank you.

Your first code sample works great. What problem are you experiencing? You can see it working here: jsbin.com/uxevi3 — Philippe Leybaert
– Philippe Leybaert, Commented Apr 15, 2010 at 10:22
@Philippe Leybaert, see eBusiness answer. I've just forget to use new. — Kirzilla
– Kirzilla, Commented Apr 15, 2010 at 10:26

aaaaaaaaaaaa · Accepted Answer · 2010-04-15 10:21:08Z

5

JavaScript is a little dodgy in this area, your code works as long as you call Dog using the new constructor.

new Dog("Hello world")

The new constructor makes this behave like you want it to. Otherwise it is totally different.

answered Apr 15, 2010 at 10:21

aaaaaaaaaaaa

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