Javascript对象创建与此关键字和prototype属性的混淆

Question

I try to create a javascript object as follows

var SuperObj = function(){
    this.super = "super from Super";
    this.prototype.getSuper = function(){
        return this.super;
   }
}

the code above throw errors:

TypeError: Cannot set property 'getSuper' of undefined

However when I tried the following code it worked.

var SuperObj = function(){
    this.super = "super from Super";
    SuperObj.prototype.getSuper = function(){
        return this.super;
    }
}

I want to know the difference. I think in the first case, both 'this' share the same execute environment. How come we can use it to add property but not function in prototype property?

Answer 1

SuperObj.prototype and this.prototype are not the same things. There is no default property called prototype on object instances.

The following will do what you are trying to do

var SuperObj = function(){
  this.super = "super from Super";
  // Here, this.constructor === SuperObj
  this.constructor.prototype.getSuper = function(){
      return this.super;
  }
}

Having said all that, I have never found a valid case for setting prototype properties during construction. Prototype properties are set once, object properties are set with every constructor. See Javascript inheritance: call super-constructor or use prototype chain?

Answer 2

When you create a new object instance you can't access to prototipe property because doesn't exist any one.

If you want to access to the prototype property through this you have to use the following pattern:

this.constructor.prototype.method