Training Guide: Programming in HTML5 with JavaScript and CSS3 Ebook

Lesson 1: Creating JavaScript objects CHAPTER 6 275

This test is successful, so replace the getInfo method and add more tests. The following

test code does this.

test("Instance Test Using Prototype and getters", function () {

expect(4);

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

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

var expected = 'Vehicle: 2000 Ford Fusion';

var actual = car1.getInfo();

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

' Actual value: ' + actual);

var expected = 'Vehicle: 2010 BMW Z4';

var actual = car2.getInfo();

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

' Actual value: ' + actual);

Vehicle.prototype.getInfo = function () {

return 'Car Year: ' + this.getYear()

+ ' Make: ' + this.getMake()

+ ' Model: ' + this.getModel();

};

var expected = 'Car Year: 2000 Make: Ford Model: Fusion';

var actual = car1.getInfo();

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

' Actual value: ' + actual);

var expected = 'Car Year: 2010 Make: BMW Model: Z4';

var actual = car2.getInfo();

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

' Actual value: ' + actual);

});

The test result is shown in Figure 6-7. You can replace the getInfo method and, because

the data is exposed as read-only, it’s available to be used in the new method. In addition, the

privileged getters are small, which minimizes the amount of memory consumed when each

instance has a copy of the method. Remember to create only getter methods as needed and

to keep them small and concise.

Quick check

■■How can you expose private data as read-only?

Quick check answer

■■Add a getter method that retrieves the data but cannot change the data.