Training Guide: Programming in HTML5 with JavaScript and CSS3 Ebook

Lesson 1: Creating JavaScript objects CHAPTER 6 273

Now that you have a functioning class, change the prototype to see whether it can be

changed across all instances.

test("Instance Test Using Prototype Replace Function", function () {

expect(2);

var car1 = new Vehicle(2000, 'Ford', 'Fusion');

var car2 = new Vehicle(2010, 'BMW', 'Z4');

Vehicle.prototype.getInfo = function () {

return 'Car: ' + this.year + ' ' + this.make + ' ' + this.model;

}

var expected = 'Car: 2000 Ford Fusion';

var actual = car1.getInfo();

equal(actual, expected, 'Expected value: ' + expected +

' Actual value: ' + actual);

var expected = 'Car: 2010 BMW Z4';

var actual = car2.getInfo();

equal(actual, expected, 'Expected value: ' + expected +

' Actual value: ' + actual);

});

This test creates two Vehicle instances and then changes getInfo. Next, the two assertions

are modified to check both instances to see whether they are using the updated getInfo. The

result is shown in Figure 6-6.

FIGURE 6-6 he modification of the getInfo prototype affected all instancesT

You might use the prototype property when creating functions that will be shared across

all instances, but remember that the prototype is defined externally to the constructor

function, so all properties must be public when using the this keyword. If you don’t need to