Building Android Apps with HTML, CSS, and JavaScript, 2nd Edition

Debugging

It can be tough to debug apps that use the offline application cache, because there’s very little visibility into what is going on. You may find yourself constantly wondering if your files have downloaded or if you are viewing remote or local resources. Plus, switching your device between online and offline modes is not the snappiest procedure and can really slow down the develop-test-debug cycle.

One thing you can do to help determine what’s going on when things aren’t playing nice is to set up some console logging in JavaScript.

Note

If you want to see what’s happening from the web server’s perspective, you can monitor its log files. For example, if you are running a web server on a Mac or Linux computer, you can open the command line and run these commands (the $ is the shell prompt, which you should not type):

$ cd /var/log/apache2/
$ tail -f access?log

This will display the web server’s log entries, showing information such as the date and time a document was accessed, as well as the name of the document. When you are done, press Control-C to stop following the log.

The ? on the second line will match any character; on Ubuntu Linux, the filename is access.log and on the Mac it is access_log. If you are using another version of Linux, the name of the file and its location may be different.

On Windows, you can find IIS7’s log files in C:\inetpub\logs, but you will need to authenticate as an administrative user to access the files (if you navigate to that folder in Windows ...