Training Guide: Programming in HTML5 with JavaScript and CSS3 Ebook

134 CHAPTER 3 Getting started with JavaScript

Answers

This section contains the answers to the lesson review questions in this chapter.

Lesson 1

1. Correct answer: C
   A. Incorrect: The undefined value means that the variable has never been initialized.
   B. Incorrect: The null value means that the variable was explicitly set to have no
   value.
   C. Correct: When performing a mathematical operation on a nonnumeric value, NaN
   (not a number) will result.
   D. Incorrect: The Infinity value will result when your value exceeds
   1.7976931348623157E + 10308.


2. Correct answers: B, C, D, and F
   A. Incorrect: You cannot use a JavaScript keyword for a variable name, and switch is a
   JavaScript keyword.
   B. Correct: The myChar variable name is valid.
   C. Correct: JavaScript allows a variable name to contain the dollar sign, so the $cost
   variable name is valid.
   D. Correct: JavaScript allows a variable name to contain the underscore, so the _total
   variable name is valid.
   E. Incorrect: Variable names cannot begin with a number.
   F. Correct: Variable names can contain numbers but cannot begin with a number.


3. Correct answer: B
   A. Incorrect: The use of ?? causes a syntax error.
   B. Correct: The use of || causes Valid User to be displayed if userName has no value.
   C. Incorrect: The use of && displays nothing if userName has no value.
   D. Incorrect: The use of + causes Valid User to be displayed if userName has no value,
   but it also displays the userName and Valid User together when the userName has
   a value.

Lesson 2

1. Correct answer: B
   A. Incorrect: QUnit is for testing JavaScript for the web, not Windows 8.
   B. Correct: QUnit-Metro is a variation of QUint, which supports Windows 8.