AJAX - The Complete Reference

PART IV

Appendix A: JavaScript Quick Reference 567

Beyond these well-known reserved words, there are other words that may have

problems under some versions of JavaScript including ECMAScript 4, Jscript.NET, and

JavaScript 2.0. While the words shown in Table A-11 may not actually be reserved in your

browser, they should be avoided just to be safe.

Also, you should be considerate of words that are found in intersections with the language,

such as values in XHTML and CSS, which may create confusion or error. Furthermore, given

that the Window object is the parent space, its properties and methods (for example, location)

should also be considered off limits for user-defined values unless being overridden.

Variables

Variables in JavaScript should be defined using the keyword var and may be defined

multiply and assigned upon definition.

var x;

var a,b,c;

var favNum = 33, favColor, favTech = "Ajax";

Given the loose type nature of JavaScript there is no ability or need in JavaScript 1.7 or

earlier to indicate the type of a variable. Some developers may name their variables to

provide some clue to their expected type, though this does not guarantee the actual value.

var strMyName, objDog, numX, boolLikeSushi;

For better or worse, JavaScript will also define variables upon their first use and put

them in the global space.

z = "I'm alive!"; // z is now defined

Variable Scope

Outside of a function or object, variables are within the global space whether explicitly

defined with var or not. Within a function or object, if the var statement is used, the defined

variable will be local to the construct; without the statement, it will be global. The following

code fragment shows these possibilities:

var global1 = true;

global2 = true;

as event is uint

assert get namespace ulong

decimal include require use

ensure internal sbyte ushort

exclude invariant set

TABLE A-11 Potentially Reserved Words