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Your Third Program
Checking values
In an if statement we test for whether something is equal by saying ==. If we want to see if something is NOT equal we use !=. These are just the rules of JavaScript. So, we can say "if indexOf returns a value of -1" like this:
if (navigator.appName.indexOf("Netscape") == -1)
We say "if index of does not return a value of -1" like this:
if (navigator.appName.indexOf("Netscape") != -1)
If again
If the value returned by indexOf is -1, we know the "Netscape" is NOT in the browser name. (That is Netscape with a capital N). But we don't know for sure that the browser name is Internet Explorer. The user could have something else. So we need to do another test, to see if "Internet Explorer" is in the browser name.
if (navigator.appName.indexOf("Internet Explorer") == -1)
If we get a -1 from indexOf in this if test, we know the name doesn't have Internet Explorer in it.
We can also write these if tests using NOT equals, !=, which will actually be a little easier. If indexOf does NOT return -1, that means the value IS in the browser name. So
if (navigator.appName.indexOf("Netscape") != -1)
means the browser is Netscape. And
if (navigator.appName.indexOf("Internet Explorer") != -1)
means the browser is Internet Explorer.
Else
If you recall from the second program discussion, an if statement gives you a way to tell the computer what to do when the if is false. The stuff to do when the if is false is signalled with the term else.
if (navigator.appName.indexOf("Netscape") != -1)
document.writeln("Hey Netscape user!");
else
document.writeln("You're not using Netscape");
In the above example, we'll print "Hey Netscape user!" to the screen if the browser name contains the value "Netscape", otherwise (else) we'll print out "You're not using Netscape". You can string along several tests together by saying else if. And you can specify one last thing to do if all of your previous if tests were false with a plain else.
if (navigator.appName.indexOf("Netscape") != -1)
document.writeln("Hey Netscape user!");
else if (navigator.appName.indexOf("Internet Explorer") != -1)
document.writeln("Hey IE user!");
else
document.writeln("You're not using Netscape or IE");
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