It's flavours and versions

Javascript, despite the name, is not part of the Java programming language developed by Sun. It was originally introduced with Netscape Navigator v2.0 and was designed to create dynamic online pages, such as checking details on html forms before allowing the page to submit the data.

Microsoft introduced their own scripting language - related to Visual Basic and called VBScript - but since the release of Internet Explorer v4 has fully supported Javascript in preference to VBScript. Because of this rivalry, Microsoft Internet Explorer v3 is NOT fully Javascript compatible and has numerous bugs and errors in the way it interprets Javascript. You would be well advised not to use Javascript in IE3 unless you have a way of testing all pages on both IE3 and IE4 as well as Netscape. To achieve this, you will need to identify the browser being used

Table of browsers and compatible Javascript versions

IE3 is decreasing in usage and most internet visitors using IE will use a more recent version. Other browsers like Konqueror, Opera and Galeon also have Javascript abilities. However, Javascript cannot be assumed to work in other browsers and may be disabled by the user. IE3 may still be in use on local intranets and there are other visitors who need to use text-only, voice-controlled or other browsers that cannot support any kind of scripting. Your use of Javascript should take into account your target audience by including <noscript> sections. Javascript is useful but it cannot replace a server-side script using PHP, Perl, Java or ASP.

Javascript also has security implications, for the user and the data. In particular, e-commerce relying on Javascript can be unreliable because of browser incompatibilities and all data handled by Javascript code is fully visible to the user. This could include sensitive data about your site. Javascript embedded in HTML format emails poses security implications for users with the result is that many users are advised to disable Javascript and VBScript. Without a secure connection (using https://), the data is also available to anyone in between the user and the site.

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