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Contents:
Writing JavaScript
Naming Rules and Conventions
A Weakly Typed Language Means That JavaScript Is Smart
As you saw in Chapter 1, "Jump-Starting JavaScript," JavaScript goes into an HTML page. However, you do not write JavaScript with the same abandon as you do HTML. Very specific and apparently minor differences exist between how HTML can be written and how JavaScript can be written. While the differences might appear to be minor or even trivial, if the rules for writing JavaScript are not followed, you can run into glitches. This chapter examines the nuances of JavaScript so that when you start writing your own scripts, you'll have all of the basics clear in your mind.
HTML is a markup language, and JavaScript is a programming or scripting language. HTML describes what is to be presented on a page, and JavaScript dynamically changes what is on an HTML page (among other tasks.) Both use code. HTML's code is in a series of angle brackets that describe how to treat the material between the opening and closing brackets. JavaScript is a set of statements and functions that does something in an HTML page. JavaScript can refer to and alter objects described by HTML.
You can write HTML tags in just about any way you want, as long as you spell the tags correctly and remember to include the arrow bracket around the tags. For example, the following little page will work just fine in HTML:
<hTmL>
<heaD>
<Title>Do it your way</tITLE>
</HEAD>
<BoDY Bgcolor="HotPink">
<ceNTer>
<h1>
HTML is CaSe InSeNsItIvE!
</H1>
</bODY>
</HTML>Just about every non–case-sensitive combination of characters that you can imagine has been put into that page. The opening tags of a container are in one case combination, and the closing tags are in another. Tags in one case are duplicated with tags in another case. For HTML, that's no problem. You don't have to pay attention to case at all.
JavaScript is the opposite. You have to pay attention to the cases of everything that you type in JavaScript because it is case-sensitive. The HTML around the script need not be case-sensitive, but the JavaScript itself must be. Consider the following examples. The first follows the rules of case sensitivity, and the second one does not.
<html>
<head>
<title>Case Sensitive</title>
<script language="JavaScript">
alert("Pay attention to your cases!");
</script>
</head>
<body bgcolor="moccasin">
<p>
<h1>Just in case!</h1>
</p>
</body>
</html>When you load the page, you will see an alert message telling you to pay attention to your cases. As soon as you click the OK button on the alert box, the rest of the page appears with the message "Just in case." Now, look at this next script to see if you can tell where the error lies. It is slightly different from the first—only the a in "alert" has been changed so that it is "Alert." Just that little change will invalidate the JavaScript code. Launch the page with the capital A, and see what happens.
<html>
<head>
<title>Case Sensitive</title>
<script language="JavaScript">
Alert("Pay attention to your cases!");
</script>
</head>
<body bgcolor="moccasin">
<p>
<h1>Just in case!</h1>
</p>
</body>
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Copyright Pearson Education and
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Created: December 10, 2001
Revised: December 10, 2001
URL: http://webreference.com/programming/javascript/jsdesign/chap2/
