JavaScript #4                                                   Instructor: Roseann Krane

JavaScript is capable of doing more functions than simply writing text to the screen. The conditional statement provides the ability to make decisions. The conditional statement evaluates a condition and then takes different actions depending on the results of that evaluation.

The keywords are if, else, and return and the condition is followed by a statement block which consists of an opening brace, statements and a closing brace. Example:

if (<condition>)
{
    statement 1;
   statement 2;
   statement N;
}
else
{
   statement e1;
   statement e2;
   statement eN;
}

The JavaScript condition will always consist of two tokens separated by a relation operator. A token can be either a variable name or a literal constant. The relational operator may be any of the following:

Operator            Meaning

==                is equal to
!=                 is not equal to
<                  is less than
>                  is greater than
<=                is less than or equal to
>=                is greater than or equal to

Task to do:  Add the following script to your page:

<SCRIPT>
        if (navigator.appName == "Netscape")
        {
                document.write ("You are using Netscape Navigator.");
        }
         else
        {
                document.write ("You are not using Netscape.<BR>");
                document.write ("I'll bet your're using Internet Explorer.");
        }
</SCRIPT>
           

JavaScript alert() will allow the program to display a special dialog box that will alert the user that an expected event has occurred, or that some kind of user input is required.  Try it:

Add the alert statement after the first document.write in your script: 

alert ("Netscape Navigator detected.");

and add a second alert to the else block:

alert ("Netscape Navigator required.");

JavaScript Events available:

Event Name        Event Trigger

onAbort                 The user aborted the loading of a Web page.
onBlur                    The user deactivated an object (the object lost focus).
onChange               The user changed an object in some way.
onClick                   The user clicked the mouse on an object.
onError                   The JavaScript interpreter encountered a script error.
onFocus                  The user activated an object (the object received focus).
onLoad                   The Web browser finished loading a page.
onMouseOver         The mouse pointer passed over an object.
onMouseOut           The mouse pointer moved off of an object.
onSelect                  The user selected (highlighted) the contents of an object.
onSubmit                 The user submitted a HTML form.
onUnload                 The Web browser unloaded a page from memory.

Task to do:

Seach the web for examples of the events which we haven't used. Send email to the teacher's class account giving the url of two examples other than onLoad or onMouseOver.