JavaScript is a simple object-oriented language specifically designed for adding interactive capabilities to Web pages. The goal of the language is to make the design of interactive Web pages as simple as possible. It provides cross platform computation and a simple interface to Java applets.
JavaScript is not a dialect or subset of Java, although the two languages do share some syntactic forms. It is a class-free object-oriented language, closer in design to Self than to Java. It is a block structured language, in the style of Pascal and Modula-2, that is procedures ("functions" in JavaScript) can contain other procedure declarations. In fact, its object structure is built on this: objects are functions whose local functions and variables are their methods and instance variables. Furthermore, functions are first class objects (well, the implementation isn't perfect), in particular there is a construct similar to the lambda form of Lisp.
JavaScript Documentation