JScript is the Microsoft implementation of the ECMA 262 language specification (ECMAScript Edition 3). With only a few minor exceptions (to maintain backwards compatibility), JScript is a full implementation of the ECMA standard.
JScript is an interpreted, object-based scripting language. It has fewer features than full-fledged object-oriented languages like C++, C#, or Visual Basic. For example, it has no built-in support for reading or writing files.
You cannot write stand-alone applications in JScript. JScript scripts run only in the presence of an interpreter or "host", such as Active Server Pages (ASP), Internet Explorer, or Windows Script Host.
JScript is a loosely typed language. In other words, you cannot declare the data types of variables explicitly. In many cases JScript performs conversions automatically when needed. For instance, if you add a number to an item consisting of text (a string), the number is converted to text.
The rest of this user's guide is an overview of JScript features. For full details of the language implementation, consult the language reference.