1.5 What Versions? What Browsers?

When a user receives a page that includes JavaScript, the script is sent to the JavaScript interpreter, which executes the script. Since each browser has its own interpreter, there are often differences on how the code will be executed. And as the competing companies improve and modify their browsers, new inconsistencies may occur. There are not only different types of browsers to cause the incompatibilities but also different versions of the same browser.

1.5.1 Versions

JavaScript has a history. Invented by Netscape, the first version was JavaScript 1.0. It was new and buggy and has long since been replaced by much cleaner versions. Microsoft has a scripting language comparable to JavaScript called JScript. The Table 1.2 lists versions of both JavaScript and JScript.

Table 1.2. JavaScript and JScript.

JavaScript or JScript Version	Browsers Supported
JavaScript 1.0	Netscape Navigator 2.0, Internet Explorer 3.0
JavaScript 1.1	Netscape Navigator 3.0, Internet Explorer 4.0
JavaScript 1.2	Netscape Navigator 4.0 “4.05, Internet Explorer 4.0
JavaScript 1.3	Netscape Navigator 4.06 “4.7x, Internet Explorer 5.0
JavaScript 1.5	Netscape Navigator 6.0+, Mozilla ( open source browser), Internet Explorer 5.5+
JScript 1.0	Internet Explorer 3
JScript 2.0	Internet Explorer 3
JScript 3.0	Internet Explorer 4
JScript 4.0	Internet Explorer 4
JScript 5.0	Internet Explorer 5
JScript 5.5	Internet Explorer 5
JavaScript is supported by Netscape 2, Explorer 3, Opera 3, and all newer versions of these browsers. In addition, HotJava 3 supports JavaScript, as do iCab for the Mac, WebTV, OmniWeb for OS X, QNX Voyager and Konqueror for the Linux KDE environment. NetBox for TV, AWeb and Voyager 3 for Amiga, and SEGA Dreamcast and ANT Fresco on RISC OS also support JavaScript.

1.5.2 Standardizing JavaScript (The EMCA Specification)

To guarantee that there is one standard version of JavaScript available to companies producing Web pages, ECMA (European Computer Manufacturers Association) is working with Netscape to provide an international standardization of JavaScript called ECMA-Script. ECMAScript is based on core JavaScript and behaves the same way in all applications that support the standard. The first version of the ECMA standard is documented in the ECMA-262 specification. After ironing out many of the inconsistencies between JavaScript and ECMA-262, JavaScript 1.3 is fully compatible with ECMA-262. The Netscape DevEdge or ECMA Web site has online documentation and PDF versions of the ECMA-262 specifications.