• Upon completing this module, the student should be able to:
  • Understand and Use Variables
  • Understand and Call Functions
  • Answer all questions at the end of Chapters 3 and 4 of the book.
  • The book makes understanding variables quite easy. We’ll add a little here:
  • Most languages have a way to define constants. A constant is a value that cannot be changed.
  • In some languages, constants are variables that are not allowed to be changed.
  • In some languages, constants are variables that should not be changed.
  • In some languages, constants look like variables, but are really just values that are used by the compiler or interpreter.
  • JavaScript does not have a way to define or use constants!

Many languages require that the type of the variable be defined. For instance, in Java you might define:
int x;
Which means to define a variable called x and to specify that it will contain an integer. These languages are “strongly typed”. JavaScript is not “typed”, because:
var x;
Can contain an integer, a floating point value, a string, or anything you like

  • Likewise, the book does a good job on functions, but here’s a little more info:
  • Many languages, especially “strongly typed” languages, make a distinction between functions and subroutines.
  • A function returns a value of a certain type
  • A subroutine does not return a value (in other words, it’s a function that does not return a value)
  • Since JavaScript is not a “strongly typed” language, there is no reason to make a distinction between functions that return a value and those that don’t.
  • Using only the techniques from modules one and two, and chapters one through four of the textbook:
  • Create two files, one named second.html and the other named second.js
  • Write code to create a web page that uses a JavaScript program to output a NASA style count down:
    Ten
    Nine
    …
    One
    Ignition Start
    Liftoff
    We have Liftoff!
  • Each line must be displayed as an alert
  • Create a generic function that outputs one line of the countdown as an alert, and receives the data to output as an input parameter.
  • Use that function to output each line of the countdown.
  • Each line, after the first line, must only be output when the user clicks “Ok” in response to the alert.
  • Use comments and lay the code out so it can be easily followed!
  • Each file in the assignment must have a comment at the top, using the correct commenting technique for the file type, like this:
    Your Name
    Your Student ID
    CST140
    Assignment 2
  • Test your program by opening the web page in your browser. You should see the NASA countdown displayed as a series of alerts (which are displayed one at a time in a popup window.) Click the OK button to display the next line in the countdown.
    No text is required to be written directly to the browser window.