Ayman Hourieh covers some interesting manipulation of Arrays that accommodates typical data structures. He also covers how to bind methods to objects, sorting with custom functions. He shows a custom AssertException, and covers using Firebug for debugging. He covers some JavaScript quirks: static local variables, null, undefined and delete.
All JavaScript implementations implement a debugger statement, which can be called at any point in your script. Also we have console.debug in Firebug.
Douglas Crockford's presentation on Advanced JavaScript. He covers topics such as inheritance, modules, debugging, efficiency and JSON.