How do I get the last line to work?
function Animal(name){
this.name = name;
}
Animal.prototype.speak = function(){
alert('Hi, I\'m ' + this.name);
}
function Dog(name){
this.name = name;
}
Dog.prototype.bark = function(){
alert('Woof!');
};
var fido = new Dog('Fido');
fido.bark(); // Woof!
fido.speak(); // Hi, I'm Fido *can't get this to work*
Dog.prototype = new Animal();
...
function Dog(name){
this.name = name;
}
Dog.prototype = Object.create(Animal.prototype);
Dog.prototype.constructor= Dog;
Dog.prototype.bark = function(){
alert('Woof!');
};
...
Object.create create a new empty object and use the parameter has prototype of this object.
You can make a inheritence in the constructor too:
function Dog(name){
Animal.call(this, name);
this.name = name;
}
Here, you call the Animal constructor on the new Dog context.
name gets initialized as instanceOfDog.name when you create it. this.name=name is no longer needed in Dog because Animal already does that. If you have a whole bunch of values that need to be validated and set then one line in Dog, Cat, Bird ... would take care of that.In short; you can do it like this:
var Dog = function(name){
//re use Animal constructor
Animal.call(this,name);
//you can do Animal.apply(this,arguments); as well
};
//set up the prototype chain
Dog.prototype = Object.create(Animal.prototype);
//repair the constructor property
Dog.prototype.constructor = Dog;
An introduction to constructor functions, inheritance and prototype can be found here.
