Beginning JavaScript with DOM Scripting and Ajax, 2nd Edition

APPENDIX A ■ Debugging JavaScript
Figure A-13. You can use the console to inspect JavaScript that has been loaded from your site
As you write JavaScript, there is one command you might use more than any other to make sure that things are
working the way you think they should:
console.log();
You used this in the try/catch example. If you have the console open, you can see the results of those statements
printed in the console. In other languages, this would be a print statement, or trace in ActionScript. What this gives
you is the ability to print messages.
For example, suppose you need to know your code executed up to a certain point or the current value of a
variable (showing image x of 10). You can do this without stopping the application from running, as you would do if
you were using a breakpoint.
JSLint and Jasmine
Some browser-independent tools are available that also can help you with JavaScript development. One is the online
JavaScript verifier JSLint by Douglas Crockford, which is available at http://www.jslint.com/lint.html. JSLint is
a tool written in JavaScript that verifies scripts in terms of syntactical validity and tries to ensure good coding style.
Because “good coding style” is a subjective matter, you might want to take JSLint reports with a grain of salt. JavaScript
development happens mostly in browser environments, and from time to time you need to bend the rules or cut
corners to make a script work faster or work around browser issues. That being said, it is still a great tool to use to find
ways to optimize your scripts in terms of cleanliness of code if you don’t have to cut corners. The great thing about
JSLint is that it gives you a full analysis of your script, including reports on global variables and how many times
different functions have been called.
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