JScript
Implementation of ECMAScript by Microsoft
title: "JScript" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["internet-explorer", "javascript-dialect-engines", "javascript-programming-language-family", "microsoft-programming-languages", "object-based-programming-languages", "prototype-based-programming-languages", "scripting-languages"] description: "Implementation of ECMAScript by Microsoft" topic_path: "technology/programming-languages" source: "https://en.wikipedia.org/wiki/JScript" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0
::summary Implementation of ECMAScript by Microsoft ::
::data[format=table title="Infobox programming language"]
| Field | Value |
|---|---|
| name | JScript |
| logo | Jscript icon.gif |
| logo size | 60px |
| paradigms | Multi-paradigm: object-oriented (prototype-based), functional, imperative, scripting |
| family | ECMAScript |
| developer | Microsoft |
| released | |
| latest release version | 9.0 |
| latest release date | |
| discontinued | yes |
| typing | dynamic, weak, duck |
| scope | lexical |
| operating system | Microsoft Windows |
| license | proprietary |
| file ext | [.js](js), .jse, [.wsf](wsf), .wsc ([.htm](htm), [.html](html), [.hta](html-application), [.asp](active-server-pages)) |
| website | |
| implementations | Active Scripting, JScript .NET |
| influenced by | JavaScript |
| :: |
| name = JScript
| logo = Jscript icon.gif
| logo size = 60px
| paradigms = Multi-paradigm: object-oriented (prototype-based), functional, imperative, scripting
| family = ECMAScript
| designer =
| developer = Microsoft
| released =
| latest release version = 9.0
| latest release date =
| discontinued = yes
| typing = dynamic, weak, duck
| scope = lexical
| operating system = Microsoft Windows
| license = proprietary
| file ext = [.js](js), .jse, [.wsf](wsf), .wsc ([.htm](htm), [.html](html), [.hta](html-application), [.asp](active-server-pages))
| website =
| implementations = Active Scripting, JScript .NET
| dialects =
| influenced by = JavaScript
| influenced =
JScript is Microsoft's legacy dialect of the ECMAScript standard that is used in Microsoft's Internet Explorer web browser and HTML Applications, and as a standalone Windows scripting language. It is proprietary software.
JScript is implemented as an Active Scripting engine. This means that it can be "plugged in" to OLE Automation applications that support Active Scripting, such as Internet Explorer, Active Server Pages, and Windows Script Host. It also means such applications can use multiple Active Scripting languages, e.g., JScript, VBScript or PerlScript.
JScript was first supported in the Internet Explorer 3.0 browser released in August 1996. Its most recent version is JScript 9.0, included in Internet Explorer 9.
JScript 10.0 is a separate dialect, also known as JScript .NET, which adds several new features from the abandoned fourth edition of the ECMAScript standard. It must be compiled for .NET Framework version 2 or version 4, but static type annotations are optional.
JScript has been criticized for being insecure and having multiple security bugs "exploited by nation-state actors", leading Microsoft to add an option to disable it.
Comparison to JavaScript
As explained by Douglas Crockford in his talk titled The JavaScript Programming Language on YUI Theater,
However, JScript supports conditional compilation, which allows a programmer to selectively execute code within block comments. This is an extension to the ECMAScript standard that is unsupported in other JavaScript implementations, thus making the above statement not fully true, although conditional compilation is no longer supported in Internet Explorer 11 Standards mode.
Other internal implementation differences between JavaScript and JScript, at some point in time, are noted on the Microsoft Developer Network (MSDN). The default type value for the script element in Internet Explorer is JavaScript, while JScript was its alias. In an apparent transition from JScript to JavaScript, online, the Microsoft Edge [Legacy] Developer Guide refers to the Mozilla MDN web reference library as its definitive documentation. As of October 2017, Microsoft MSDN pages for scripting in Internet Explorer are being redirected there as well. This information may not include JScript specific objects, such as Enumerator, which are listed in the JavaScript language reference on Microsoft Docs. Those provide additional features that are not included in the ECMA Standards, whether they are supported in the Edge [Legacy] browser or its predecessor.
Versions
JScript (COM Classic)
The original JScript is an Active Scripting engine. Like other Active Scripting languages, it is built on the COM/OLE Automation platform and provides scripting capabilities to host applications.
This is the version used when hosting JScript inside a Web page displayed by Internet Explorer, in an HTML application before IE9, as well as in classic ASP, Windows Script Host scripts and other Automation environments.
JScript is sometimes referred to as "classic JScript" or "Active Scripting JScript" to differentiate it from newer .NET-based versions.
Some versions of JScript are available for multiple versions of Internet Explorer and Windows. For example, JScript 5.7 was introduced with Internet Explorer 7.0 and is also installed for Internet Explorer 6.0 with Windows XP Service Pack 3, while JScript 5.8 was introduced with Internet Explorer 8.0 and is also installed with Internet Explorer 6.0 on Windows Mobile 6.5.
Microsoft's implementation of ECMAScript 5th Edition in Windows 8 Consumer Preview is called JavaScript and the corresponding Visual Studio 11 Express Beta includes a "completely new", full-featured JavaScript editor with IntelliSense enhancements for HTML5 and ECMAScript 5 syntax, "VSDOC" annotations for multiple overloads, simplified DOM configuration, brace matching, collapsible outlining and "go to definition".
::data[format=table]
| Version | Date | Introduced with | Based on | Similar JavaScript version |
|---|---|---|---|---|
| 1.0 | Aug 1996 | Internet Explorer 3.0 | Netscape JavaScript | 1.0 |
| 2.0 | Jan 1997 | Windows IIS 3.0 | Netscape JavaScript | 1.1 |
| 3.0 | Oct 1997 | Internet Explorer 4.0 | ECMA-262 1st edition | 1.3 |
| 4.0 | Visual Studio 6.0 (as part of Visual InterDev) | ECMA-262 1st edition | 1.3 | |
| 5.0 | Mar 1999 | Internet Explorer 5.0 | ECMA-262 2nd edition | 1.4 |
| 5.1 | Internet Explorer 5.01 | ECMA-262 2nd edition | 1.4 | |
| 5.5 | Jul 2000 | Internet Explorer 5.5 & Windows CE 4.2 | ECMA-262 3rd edition | 1.5 |
| 5.6 | Oct 2001 | Internet Explorer 6.0 & Windows CE 5.0 | ECMA-262 3rd edition | 1.5 |
| 5.7 | Nov 2006 | Internet Explorer 7.0 | ECMA-262 3rd edition + ECMA-327 (ES-CP) | 1.5 |
| 5.8 | Mar 2009 | Internet Explorer 8.0 & Internet Explorer Mobile 6.0 | ECMA-262 3rd edition + ECMA-327 (ES-CP) + JSON (RFC 4627) | 1.5 |
| 11.0 | Jun 2024 | Windows 11 version 24H2 | (JScript 9 Legacy, designed as a compatible drop-in replacement for JScript 5.8, but not 100% compatible) | 1.5 |
| :: |
JScript is also available on Windows CE (included in Windows Mobile, optional in Windows Embedded CE). The Windows CE version lacks Active Debugging.
Managed JScript
Managed JScript is an implementation of JScript for the Dynamic Language Runtime, it is part of Microsoft's dynamic languages for .NET along with IronRuby, IronPython, and Dynamic Visual Basic. Unlike JScript .NET, which is less dynamic than the original JScript but provides Common Language Infrastructure (CLI) compatibility, Managed JScript is designed on top of the Dynamic Language Runtime (DLR) and provides the features needed for scripting scenarios.
While it is primarily designed to be used within Silverlight and ASP.NET at this time, it can also easily be embedded within any .NET application.(Source: JScript Blog, Jim Hugunin's Thinking Dynamic blog, Source: Blog of Jitu)
Two builds of Managed JScript exist: one for the Desktop Common Language Runtime (CLR) and one for the Silverlight CoreCLR ::data[format=table]
| Version | Date | Introduced with | Based on | Platform |
|---|---|---|---|---|
| 1.0.0.0 | 2007 | ASP.NET Futures (July 2007 preview) | ECMA-262 3rd edition | Desktop CLR 2.0 |
| 1.1.20625.0 | 2007 | Microsoft Silverlight 1.1 Alpha (Sep 2007 refresh) | ECMA-262 3rd edition | CoreCLR 1.1 |
| :: |
Managed JScript is unsupported in the .NET Compact Framework.
(Source: files versions of Microsoft.JScript.Runtime.dll in ASP.NET Futures and Silverlight 1.1 folders)
JScript "Chakra" (JsRT)
JScript "Chakra" is based on the JScript (COM classic) version, but it has been redesigned to improve performance in Internet Explorer 9 at the expense of proper Active Scripting engine compatibility. It requires a specific Microsoft JavaScript Hosting (JsRT) API for proper use. Therefore, it is installed side by side with JScript 5.x and is only used by Internet Explorer 9 and later as well as JsRT hosts, while other Active Scripting hosts keep using the 5.x version when requesting the JScript engine.
::data[format=table]
| Version | Date | Introduced with | Based on | Similar JavaScript version |
|---|---|---|---|---|
| Chakra 9.0 | Mar 2011 | Internet Explorer 9.0 | ECMA-262 5th edition | 1.8.1 |
| Chakra 10.0 | Sep 2012 | Internet Explorer 10.0 | ECMA-262 5.1 edition | |
| Chakra 11.0 | Oct 2013 | Internet Explorer 11.0 | ECMA-262 6th edition | |
| Chakra Edge | Jul 2015 | [Edge Legacy] / Windows 10 | ECMA-262 5.1 to 9 (2018) edition | |
| :: |
There are two versions of the Chakra JsRT engine. The original one was used by Internet Explorer 9 and later, and is sometimes referred to as "jscript9.dll" or "legacy Chakra engine", and a second one used by Microsoft Edge Legacy browser and sometimes referred to as "new Chakra engine", "Edge engine" or "Chakra.dll". Both Chakra JsRT versions can be used by other applications using the JsRT API and can be installed side by side.
There is also a COM Classic version of Chakra internally called "JScript 9 Legacy" (provided by jscript9Legacy.dll), introduced with Windows 11 24H2, which brings back compatibility with Active Scripting hosts and intended as a compatible drop-in replacement for JScript 5.8. Although largely compatible with the original JScript 5.8, there are notable breaking differences.
See separate page about new Chakra (Edge) engine.
JScript .NET (CLI)
Main article: JScript .NET
JScript .NET is a Microsoft .NET implementation of JScript. It is a CLI language and thus inherits very powerful features, but lacks many features of the original JScript language, making it inappropriate for many scripting scenarios. JScript .NET can be used for ASP.NET pages and for complete .NET applications, but the lack of support for this language in Microsoft Visual Studio places it more as an upgrade path for classic ASP using classic JScript than as a new first-class language.
::data[format=table]
| Version | Platform | Date | Introduced with | Based on |
|---|---|---|---|---|
| 7.0 | Desktop CLR 1.0 | 2002-01-05 | .NET Framework 1.0 | ECMA-262 3rd edition |
| 7.1 | Desktop CLR 1.1 | 2003-04-01 | .NET Framework 1.1 | ECMA-262 3rd edition |
| 8.0 | Desktop CLR 2.0 | 2005-11-07 | .NET Framework 2.0 | ECMA-262 3rd edition |
| 10.0 | Desktop CLR 4.0 | 2010-08-03 | .NET Framework 4.0 | ECMA-262 3rd edition |
| :: |
JScript .NET is unsupported in the .NET Compact Framework.
JScript .NET versions are unrelated to classic JScript versions, and are a separate product line. Even though JScript .NET is unsupported within the Visual Studio IDE, its versions are in sync with other .NET languages versions (C#, VB.NET, VC++) that follow their corresponding Visual Studio versions.
.NET Framework 3.0 and 3.5 are built on 2.0 and do not include the newer JScript.NET release (version 10.0 for .NET Framework 4.0).
(Source: file version of jsc.exe JScript.NET compiler and Microsoft.JScript.dll installed with .NET Framework)
Notes
References
References
- (24 October 2011). "Types of Script Files". Msdn.microsoft.com.
- (2020-10-13). "Disabling legacy scripting engine JScript in Internet Explorer".
- (24 October 2011). "JScript (ECMAScript3)". Msdn.microsoft.com.
- (24 October 2011). "What Is WSH?". Msdn.microsoft.com.
- [https://msdn.microsoft.com/en-us/library/xkx7dfw1.aspx What is JScript 10.0?]
- Cimpanu, Catalin. "Microsoft adds option to disable JScript in Internet Explorer".
- "Option to disable JScript execution in Internet Explorer".
- Douglas Crockford, ''The JavaScript Programming Language''
- (15 August 2007). "The World of JScript, JavaScript, ECMAScript". Blogs.msdn.microsoft.com.
- "script element". Msdn.microsoft.com.
- "Microsoft-Edge Dev-Guide". Docs.microsoft.com.
- (18 October 2017). "Documenting the Web Together". Blogs.windows.com.
- "Javascript Language Reference (Microsoft Docs)". Docs.microsoft.com.
- "JavaScript Objects (Microsoft Docs)". Docs.microsoft.com.
- (13 May 2022}}
{{cite web). "What's New in ASP.NET 4.5 and Visual Web Developer 11 Beta: The Official Microsoft ASP.NET Site". - "Version Information (Windows Scripting – JScript)". Microsoft.
- "Microsoft JScript Features – Non-ECMA (Windows Scripting – JScript)". Microsoft.
- (1997-06-30). "Microsoft Embraces ECMA Internet Scripting Standard; Delivers Industry's First ECMA-Compliant Scripting Language, JScript 3.0, In Key Microsoft Products". Microsoft.
- "JScript Deviations from ES3". Situation Publishing / Microsoft.
- "Windows 11 22H2 has a different way of using the JS engine? - Microsoft Q&A".
- (18 March 2010). "The New JavaScript Engine in Internet Explorer 9". Microsoft.
- "Version Information (Windows Scripting – JScript)". Microsoft.
- "Internet Explorer Standards Support Documents". Microsoft.
- "Targeting Microsoft Edge vs. Legacy Engines in JsRT APIs". Microsoft.
- "Windows 11 22H2 has a different way of using the JS engine? - Microsoft Q&A".
- "What Is JScript .NET?". Microsoft.
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