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JavaScript Verifier

As you can see, this reduces the amount of code contained in the

divide()

function and also makes it

clearer what the developer was thinking when writing this function.

The JavaScript Verifier

Douglas Crockford, a software engineer, wrote a small tool called jslint — The JavaScript Verifier. The

purpose of jslint is to point out unprofessional JavaScript syntax and possible syntax errors. You simply

paste your JavaScript code (either pure JavaScript code or code enclosed in a

tag) into a text

box and click the jslint button. The tool then outputs warnings and errors about your code underneath.

The types of warnings provided by jslint are in line with the professional standards mentioned through-

out this book. You receive a warning if the code contains an inappropriate coding technique, such as the

following:

A statement (

for

while

, and so on) that doesn’t use block notation (see Chapter 2,

“ECMAScript Basics”)

A line that doesn’t end with a semicolon

var

statement declaring a variable name that is already in use

The

with

statement (for reasons to avoid

with

, see Chapter 2)

The JavaScript Verifier is available online at

http://www.crockford.com/javascript/jslint.html

and it can also be downloaded in its original source code for your own use.

Debuggers

Programmers used to developing in languages such as C, C++, Java, and Perl know that debugging is

an important part of the development process. These developers rely heavily on debuggers for such pro-

gramming languages to aid in tracking down errors in their code. Most languages offer some type of

debugger, from simple command line programs to exhaustive GUI layouts. Although JavaScript itself

doesn’t have a debugger, both Internet Explorer and Mozilla have debuggers available.

Microsoft Script Debugger

The Microsoft Script Debugger is a free utility available from Microsoft’s Web site. To download it, go to

http://www.microsoft.com/downloads/search.aspx?categoryid=10

and type

script debugger

into the Search box. The results list comes up with Script Debugger for Windows NT, 2000, XP. Click that

link and click the Download button. Run the installation program and then restart Internet Explorer.

Notice a new menu item that appears under the View menu called Script Debugger. This provides

options for running the debugger.

Running

You can run the Microsoft Script Debugger in a number of ways. First, you can open it directly by select-

ing View

Script Debugger

Open, which opens the debugger with no information loaded. The second

method is to select View

Script Debugger

Break at Next Statement, which opens the debugger before

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