View source for JScript .NET

{{Short description|Programming language developed by Microsoft}}
{{Multiple issues|
{{No footnotes|date=November 2013}}
{{Update|date=June 2015}}
}}
{{Infobox programming language
| name = JScript .NET
| paradigms = [[Comparison of multi-paradigm programming languages|Multi-paradigm]]: [[Object-oriented programming|object-oriented]] ([[Prototype-based programming|prototype-based]]), [[Functional programming|functional]], [[Imperative programming|imperative]], [[Scripting language|scripting]]
| family = [[ECMAScript]]
| designer = 
| developer = [[Microsoft|Microsoft Corporation]]
| released = <!-- {{Start date and age|20yy}} -->
| latest release version = 
| latest release date = 
| typing = [[Duck typing|duck]], [[Strong and weak typing|weak]], [[Dynamic typing|dynamic]]
| scope = [[Scope (computer science)|lexical]]
| platform = [[.NET]] framework
| operating system = [[Microsoft Windows]]
| license = [[Proprietary software|proprietary]]
| file ext = .js
| file format = JScript .NET
| website = <!-- {{URL|www.example.com}} -->
| implementations = 
| dialects = 
| influenced by = [[JavaScript]], [[JScript]], [[ECMAScript]]
| influenced = 
}}
'''JScript .NET''' is a [[.NET]] framework [[programming language]] developed by [[Microsoft]] as [[proprietary software]].

The main differences between [[JScript]] and JScript .NET can be summarized as:

Firstly, JScript is a [[scripting language]], and as such, [[computer program|programs]] (or more suggestively, scripts) can be executed with no need to [[Compiler|compile]] the code before. This is not the case with the JScript .NET [[command-line interface]] compiler, since this next-generation version relies on the .NET [[Common Language Runtime]] (CLR) for execution, which requires that the code be compiled to [[Common Intermediate Language]] (CIL), formerly named Microsoft Intermediate Language (MSIL), code before it can be run. Nevertheless, JScript .NET still fully supports [[Interpreter (computing)|interpreting]] [[source code]] at [[Execution (computing)#Runtime|runtime]] (e.g., via the <code>Function</code> constructor or the <code>[[eval#JavaScript|eval]]</code> function) and indeed the interpreter can be exposed by custom applications hosting the JScript .NET engine via the VSA{{Technical inline|reason=more on VSA interfaces|date=February 2012}} interfaces.

Secondly, JScript has a strong foundation in Microsoft's [[ActiveX]] and [[Component Object Model]] (COM) technologies, and relies mainly on ActiveX components to provide much of its function (including database access via [[ActiveX Data Objects]] (ADO), file handling, etc.), whereas JScript .NET uses the [[.NET]] framework to provide equivalent function. For backward-compatibility (or for where no .NET equivalent library exists), JScript .NET still provides full access to ActiveX objects via .NET and [[COM Interop]] using both the ActiveXObject constructor and the standard methods of the .NET <code>Type</code> class.

Although the .NET framework and languages such as [[C Sharp (programming language)|C#]] and [[Visual Basic (.NET)]] have been adopted widely, JScript .NET has received little attention, from the media and developers. It is not supported in Microsoft's premier development tool, [[Visual Studio .NET]]. However, [[ASP.NET]] supports JScript .NET.

== Language differences ==
The following are prime examples of language differences between JScript .NET and other .NET languages, including comparisons.

=== Differences with C# ===
* JScript .NET does not require an [[entry point]] ({{code|main()}} [[Function (computer programming)|function]]) that an [[operating system]] must call directly when executing a JScript .NET application, as such, JScript .NET program [[control flow]] can be based on global code.
* JScript .NET, because of its very loose [[data type]] checking system, can be easier to learn, since the common convention of [[Declaration (computer programming)|declaring]] types explicitly is unneeded.
* JScript .NET does not require explicit references to the .NET framework Base Class Library, as certain functions found in earlier versions of JScript are present in JScript .NET (e.g., functions for finding the [[Trigonometric function|tangent]] of an angle for a [[right triangle]]).
* JScript .NET is closely linked to [[C syntax]], and is thus easy to learn for [[C Sharp (programming language)|C#]], [[Java (programming language)|Java]], or [[C++]] developers.
* While JScript .NET can be used to create Windows Forms applications, it can have some trouble, as delegates can only be consumed in JScript .NET and not created. Thus, custom events are hard to emulate in JScript .NET.

=== Differences with C++ ===
* JScript .NET does not need a {{Mono|[[entry point|main()]]}} [[Function (computer programming)|function]].
* JScript .NET does not need explicit [[type declaration]] on variables. (In [[C++]], the use of templates and generics can be compared to this, loosely emulated with template specialization, etc.)
* JScript .NET does not need explicit [[Type conversion|type casts]] on variable use in the program. Code used to retrieve a string of characters, but only used for integer numbers can be cast implicitly; the vice versa can be done without error at [[compile time]], but there is a chance of loss of precision or data.
e.g.:
<syntaxhighlight lang="typescript">
import System;

Console.WriteLine("Hello, what's your name?");
Console.WriteLine("Type your name: ");

var name: String = Console.ReadLine();

Console.WriteLine($"Hello, {name}");
</syntaxhighlight>

=== Differences with Java ===
* JScript .NET syntax and lexical conventions are similar to [[Java (programming language)|Java]] in that both are derived from [[C (programming language)|C]]. JScript was originally Microsoft's implementation of [[ECMAScript]], which is more commonly known as [[JavaScript]], though it is unrelated to Java. Thus, users of Java and other C-derived languages will find JScript easier to learn.
* JScript .NET allows developers to use [[Variable (computer science)#Typing|untyped variables]], and can sometimes infer their type from their usage to optimize the compiled code. On the other hand, Java requires all variables to be typed, though Java also supports type inference.
* JScript .NET can add properties and methods to objects in [[Run time (program lifecycle phase)|run-time]], while Java objects always conform to their declared interface.
* JScript .NET supports [[global variables]], which Java does not.

=== Differences with older versions of JScript ===
* JScript .NET allows declaring variables and functions with type information (e.g., <code>var x: String;</code>), while type information for JScript's variables and functions cannot be declared (e.g., <code>var x;</code>).
* JScript .NET scripts are not interpreted, but executed independently. When executed, a JScript .NET application will invoke the [[Common Language Runtime|CLR]]. The CLR will execute the [[Common Intermediate Language|CIL]] instructions without using an interpreter.
* JScript .NET can be run without the presence of a browser or another [[Scripting language|scripting engine]] as the compiler can generate standalone [[executable]]s and assemblies. However these still require [[.NET]] framework to be installed to run.
* JScript .NET provides access to the .NET framework [[Base Class Library]] (BCL), providing much more function.
* JScript .NET is available as a scripting language for only [[ASP.NET]], the technology used to generate web pages. Thus, JScript .NET has a role similar to [[PHP]] and other [[Client–server model|server-side]] scripting languages. Internet Explorer, however, still uses only the older JScript engine, so JScript.NET cannot be used to script web pages (or [[HTML Application]]s (HTAs), or HTCs). In this regard, JScript is much more versatile than JScript .NET.

== See also ==
* [[JS++]]
* [[TypeScript]]
* [[JavaScript OSA]] – system-level scripting language for [[Apple Inc.|Apple]] [[Mac (computer)|Macintosh]]
* [[JScript]]
* [[ActionScript]]
* [[C Sharp (programming language)|C#]]

== Notes ==
{{Reflist}}

== References ==
* [http://msdn.microsoft.com/en-us/library/3bf5fs13.aspx Getting Started With JScript .NET]
* [http://msdn.microsoft.com/en-us/library/ms974588.aspx Introducing JScript .NET]
* [https://web.archive.org/web/20091027083329/http://geocities.com/Jeff_Louie/jscript_net_windows_form.htm JScript.NET tutorial and form tutorial]

{{Common Language Infrastructure}}
{{ECMAScript}}

{{DEFAULTSORT:Jscript .Net}}
[[Category:.NET programming languages]]
[[Category:JavaScript dialect engines]]
[[Category:JavaScript programming language family]]
[[Category:Object-based programming languages]]
<!-- Hidden categories below -->
[[Category:Articles with example JavaScript code]]