[4] It also means such applications can use multiple Active Scripting languages, e.g., JScript, VBScript or PerlScript.

JScript has been criticized for being insecure and having multiple security bugs "exploited by nation-state actors",[6] leading Microsoft to add an option to disable it.

As explained by Douglas Crockford in his talk titled The JavaScript Programming Language on YUI Theater, [Microsoft] did not want to deal with Sun Microsystems about the trademark issue, and so they called their implementation JScript.

[8]However, JScript supports conditional compilation, which allows a programmer to selectively execute code within block comments.

Other internal implementation differences between JavaScript and JScript, at some point in time, are noted on the Microsoft Developer Network (MSDN).

[9] The default type value for the script element in Internet Explorer is JavaScript, while JScript was its alias.

[12] This information may not include JScript specific objects, such as Enumerator, which are listed in the JavaScript language reference on Microsoft Docs.

[13] Those provide additional features that are not included in the ECMA Standards, whether they are supported in the Edge [Legacy] browser or its predecessor.

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".

(Source: files versions of Microsoft.JScript.Runtime.dll in ASP.NET Futures and Silverlight 1.1 folders) JScript "Chakra" is based on the JScript (COM classic) version, but it has been redesigned to improve performance in Internet Explorer 9[22] at the expense of proper Active Scripting engine compatibility.