All JavaScript implementations implement a debugger statement, which can be called at any point in your script. Also we have console.debug in Firebug.
First in a series of talks from Douglas Crockford about the JavaScript language. These talks cover the JavaScript language, from the history, the language, advanced features, platforms, standards and programming style. Talks about inheritance, using functions to build objects, closures, as well as the basic JavaScript syntax. Also covers code conventions. JavaScript is a language that requires discipline.
Although JavaScript is a class-free, object-oriented language using prototypal inheritance, it can still be used in a classical object-oriented way. Douglas Crockford compares the two inheritance-based systems, adding syntactic sugar to JavaScript to allow classical inheritance, and demonstrates a number of patterns that are not available in classical languages.