July 2000 Draft JavaScript 2.0 Introduction

Thursday, November 11, 1999

• Motivation
• Notation

JavaScript 2.0 is the next major step in the evolution of the JavaScript language. JavaScript 2.0 incorporates the following features in addition to those already found in JavaScript 1.5:

• Class definition syntax, both static and dynamic
• Packages, including a versioning mechanism
• Types for program and interface documentation
• Invariant declarations such as const and final
• private, package, public, and user-defined access controls
• Introspection facilities
• Overridable basic operators such as + and [ ]
• Machine types such as int for more faithful communication with other programming languages

These facilities reinforce each other while remaining fairly small and simple. Unlike in Java, the philosophy behind them is to provide the minimal necessary facilities that other parties can use to write packages that specialize the language for particular domains rather than define these packages as part of the language core.

The versioning and access control mechanisms make the language is suitable for programming-in-the-large.

The language remains firmly in the dynamic camp. Classes can be declared statically or dynamically. JavaScript 2.0 provides introspection facilities. In some ways JavaScript 2.0 is more dynamic than JavaScript 1.5. For example, it is much easier to conditionally declare functions in JavaScript 2.0 than in 1.5: one simply defines a function inside a conditional.

The overridable basic operators can be used to implement numbers with attached units similar to the Spice proposals. Rather than implement the full unit model in the language core, JavaScript 2.0 provides the syntactic and semantic hooks to allow one to implement a unit library with whatever sophistication one's application requires.

Waldemar Horwat Last modified Thursday, November 11, 1999