Overview of JScript .NET

JScript .NET is an evolution of JavaScript, or Microsoft's JScript. It is fully backwards compatible with previous versions of JScript, while providing access to the common language runtime and .NET Framework. JScript .NET is the Microsoft implementation of the ECMA 262 language (ECMAScript -- more commonly known as JavaScript). JScript .NET is being developed in conjunction with ECMAScript Edition 4. The main additions in JScript .NET are:

• Compiled code
• Typed and typeless variables
• Late- and early-binding
• Classes (inheritance, function overloading, etc)
• Packages
• Cross-language support
• Access to .NET Framework

JScript .NET programs can be used both as a script or as compiled code. A Web browser runs JScript .NET scripts embedded in a Web page. Windows Script Host runs a script that is embedded in an ASP or ASP.NET page. ASP.NET runs compiled code of JScript .NET.

JScript .NET is a true object-oriented language that still keeps its "scripting" feel, by supporting typeless programming, dynamic code execution (using eval), and more. In previous versions, the loosely typed structure of JScript meant that variables assumed the type of the value assigned to them. In fact, there was no way to declare the data types of variables in previous versions. JScript .NET allows variables to be typed. You can now bind a variable to a particular data type, and the variable can store only data of that type. Strong typing in a programming language has several benefits, such as improved execution speed, type checking, and self-documenting code.

One of the main enhancements in JScript .NET is its class-based objects. In previous versions, JScript supported inheritance through prototype-based objects. JScript .NET also supports class-based objects by explicit declaration of classes with data and behavior. Classed created in JScript .NET can be used and extended by any .NET language. Classes can inherit the properties and methods of a base class.

Namespaces are also new in JScript .NET. Namespaces prevent naming conflicts by organizing classes, interfaces, and methods into hierarchies. You can define your own namespaces in JScript .NET. You can also access any .NET Framework namespace with JScript .NET. The package statement is also new in JScript .NET. It enables packaging of related classes for easy deployment and for avoiding naming collisions.

JScript .NET inherited two more structures from C++. First, it introduces a const statement that defines an identifier that represents a constant value. JScript .NET also introduces the enum statement that allows you to construct enumerated data types. Enumeration enables you to specify helpful names for your data type values.