Simple Program: Printing a Line of Text in a Web Page

This section provides an overview of a very simple JavaScript program: a one line script that just puts some text on a web page. This page doesn't really do anything very useful; it would be easier to just put the <h1>Welcome toJavaScript Programming!</h1> content directly on the page, not in a script tag. But the purpose of this example isn't to be "useful"; it is to provide a very simple illustration of how a "script" fits into a web page, and one simple thing you can do in a script: put content on the web page.

Make sure you understand this page thoroughly. It is simple enough that you should be able to understand each and every part of it. If you do, you'll have an easier time with more complex pages later.

Another important concept from this section is the idea that the JavaScript interpreter is built into the web browser. The book mentions Internet Explorer by name, but in fact a JavaScript interpreter is built into Firefox as well, and every other web browser that supports JavaScript. The JavaScript interpreter is the part of the web browser that parses the JavaScript commands, and either reports syntax errors if any, or carries out the commands.

A few of the callouts in this section are worth noting:

Be sure to check this one out. In general, it is important when writing XHTML code to make it readable by humans as well as by the Web Browser.

The recommendation to enclose script tags is found in many textbooks and tutorials on JavaScript, and the authors repeat it here. However, this recommendation is not universally shared. I'm not advocating against it, just making you aware that designers differ on whether it is a good idea or not. See for example, the following:

http://www.netmechanic.com/news/vol6/javascript_no12.htm

http://developer.mozilla.org/en/docs/Properly_Using_CSS_and_JavaScript_in_XHTML_Documents

The definition of the following synonomous terms is in this section, so be sure to locate the definition of these terms:

string
character string
string literal
message

The authors state: "Strings in JavaScript can be enclosed in either double quotation marks (") or single quotation marks.(')." A useful point, but I'm not sure it rises to the exalted level of a "software engineering observation".

The paragraph near the top of p. 178 includes several important terms related to object-oriented programming. Compare this discussion with that on pp. 36-39, 45, and 51-52 of your Essentials For Design: JavaScript, Level 1 book.

object
attributes (data)
behaviors (methods)
arguments (also called parameters)

Note that the user of the word "attributes" in the lingo of object-oriented programming is subtly different from the use of the word "attributes" as it pertains to an HTML element. Here the word is more like the use of the word "properties" on p. 51 of your Essentials for Design JS1 book.

Several of the callouts in this section contain some interesting points:

Semicolons aren't always required in JavaScript, but it is a good idea to always use them anyway for clarity. Please always include them in the JavaScript code you write for this course.

Several of the callouts in this section contain some interesting points:

Hiding inside this callout is the definition of "case senstivity", "syntax error", and some tips on how to get JavaScript errors to show up in Internet Explorer. Be sure to read over this!

This one is a really useful tip. Watch for this one in class or in your programming. I'll give some extra credit points to the first person that emails me a really good example of this, or points one out during lecture and makes reference to this "Error Prevention Tip". (This will also tell me who is reading the reading notes and the textbook.)

The use of \" is mentioned in this section, as is are the following terms, which you should know for the exam:

escape character
escape sequence

Watch out for this; you can't do italics or bold or such in alert boxes. Only plain text: HTML or XHTML tags will just be passed right on through.