Object-Oriented JavaScript - Third Edition

Chapter 5, Prototype

Lets try and solve the following exercise:

Exercises

1. Create an object called shape that has a type property and a getType() method:

           var shape = { 
             type: 'shape', 
             getType: function () { 
               return this.type; 
             } 
           }; 
   

2. The following is the program for a Triangle () constructor:

           function Triangle(a, b, c) { 
             this.a = a; 
             this.b = b; 
             this.c = c; 
           } 
    
           Triangle.prototype = shape; 
           Triangle.prototype.constructor = Triangle; 
           Triangle.prototype.type = 'triangle'; 
   

3. To add the getPerimeter() method, use the following code:

           Triangle.prototype.getPerimeter = function () { 
             return this.a + this.b + this.c; 
           }; 
   

4. Test the following code:

    > var t = new Triangle(1, 2, 3); > t.constructor === Triangle; true > shape.isPrototypeOf(t); true > t.getPerimeter(); 6 > t.getType(); ...