C.1 Core Language Changes

There have been quite a few additions and improvements to the core JavaScript language, and to the way that it is embedded in HTML files:

• The typeof and void operators have been added. See Chapter 4, Expressions and Operators.

• The constructor property of all objects completements the typeof operator as a way to determine the type of objects. (The type property the Element object serves a similar purpose for HTML form elements). See Chapter 7, Objects and the Object.constructor reference entry.

• Constructor functions may now have a prototype object that defines methods, constants, and default properties shared by all objects created by the constructor. See Chapter 7, Objects, and the Object.constructor reference entry.

• The String object is now a true JavaScript object, with a constructor, and a new split() method.

• The Boolean and Number objects have been added. The Number object defines several useful constants.

• The Function object now supports a constructor for the creation of "anonymous" functions. See Chapter 6, Functions.

• The Array object provides a useful constructor for the creation of arrays, and also new sort(), reverse(), and join() methods. Array handling in JavaScript 1.1 is much improved over JavaScript 1.0. See Chapter 8, Arrays.

• The Math.random() method works on all platforms in JavaScript 1.1, and the Not-a-Number value, NaN, and the isNaN() function are implemented on all palatforms. This means that parseInt() and parseFloat() can now correctly return NaN to signal invalid input.

• The eval() function of JavaScript 1.0 has become a method of all objects in JavaScript 1.1. This allows JavaScript code to be evaluated in the context of any desired object. When used as a function in JavaScript 1.1, eval() will evaluate the code in the context of the current window, just as it did in JavaScript 1.0.

• All objects can now be given an assign() method, which essentially overloads the assignment operator for that particular object. See Chapter 7, Objects.

• Files of pure JavaScript code, given the .js file extension, may now be included within HTML files with the SRC attribute of the <SCRIPT> tag. See Chapter 10, Client-Side Program Structure.

• You can specify code that requires JavaScript 1.1 and should not be run on JavaScript 1.0 platforms with the LANGUAGE="JavaScript1.1" attribute of the <SCRIPT> tag. See Chapter 10, Client-Side Program Structure.

• JavaScript code can also be embedded within HTML tags between &{ and }; using the new JavaScript entity. See Chapter 10, Client-Side Program Structure.