Lesson Eight: Parameters

1. Your current JavaScript file should look like this:

   var event1;
   event1 = "488 Million Years Ago the Mollusks Appeared";
   var event2 = "250 Million Years Ago the Dinosaurs Appeared";
   var event3 = "65 Million Years Ago - Age of the Mammals";
   var event4 = "60 Million Years Ago - The Primates";
   var event5 = "5.2 Million Years Ago - The Hominids";
   var eventchoice = 4;
   
   function historyevents() {
   if (eventchoice == 1) { document.write(event1); }
   else if (eventchoice == 2) { document.write(event2); }
   else if (eventchoice == 3) { document.write(event3); }
   else if (eventchoice == 4) { document.write(event4); }
   else { document.write(event5); }
   }
   
   historyevents();

   
   
   
2. You are going to set the value of the eventchoice variable with a function parameter; so remove the = 4 code from the variable statement on line seven. Line seven should now read: var eventchoice;.
3. Parameters are values that are passed into a function. Parameters are placed inside the () parenthesis that are included with the function statement. Parameters are also variables. Add the eventnumber parameter as shown below:

   function historyevents(eventnumber) {

   
   
   
4. Set the value of the eventchoice variable by adding this code after the above line:

   function historyevents(eventnumber) {
   eventchoice = eventnumber;

5. Now you can pass the value of the eventchoice variable in the paranthesis of the function calling code:

   historyevents(4);

   
   Test your program with the new code. Your page should look like this: Sample
6. Experiment by putting different values in the calling code parameter and executing your program.

Lesson Nine: The Button Object