Debug JavaScript

When programming with JavaScript it may be necessary to debug functions, get to the roots of error messages and warnings and check variables'values.
1 answer

Use Firefox Add-On Firebug

For JavaScript debugging one can use the Firefox add-on Firebug.
To install the add-on: go to the 'Firefox' button in the browser, select 'add-ons', then search for 'Firebug' using the search engine and consequently install the add-on.
After restarting Firefox go to the 'Firefox' button again, select 'Web Developer', 'Firebug', 'Open Firebug'. Then the Firebug panel will open in the lower side of the opened tab. There select 'Script' and 'Enable' and you are ready to start debugging.
To debug you can insert breakpoints and then reload the page. It will break when encountering the line. Then you have the possibility to see variable values, continue running the script, enter, skip or exit functions etc.