AJAX - The Complete Reference

568 Part IV: Appendixes

function myFunc()

{

var local1 = "Locals only";

global3 = true;

}

Commonly, JavaScript developers make assumptions about scoping rules with var that

aren’t quite true. For example, a var statement found within a for loop does not scope that

value to the loop. In this case, j is scoped to either the function it is within or the global

space if it is outside a function or object.

for (var j = 0; j < 10 ; j++)

{ /* loop body */ }

Further, within a block, a var statement does nothing different than it would otherwise:

if (true)

{

var x = "Not block local!";

}

Under JavaScript 1.7 as supported in Firefox 2+, we see the introduction of the let

statement, which makes things a bit more complicated. You can locally bind values to the

scope of a let statement and accomplish exactly the two aforementioned ideas:

for (let j = 0; j < 10 ; j++)

{ /* loop body with j being loop local */

if (true)

{

let x = "I am block local!";

}

Constants

There are no user-defined constants in JavaScript 1.X implementations. For style concerns, if

you treat a variable as a constant you should consider casing it in all capitals:

LUCKYNUMBER = 3; // fake constant

NNOT EOTE We didn’t use the var here, though it is global, because that keyword actually hurts

readability.

Operators

JavaScript has a wealth of operators that are similar to other C-like languages, but with

some additions to deal with weak typing and some omissions due to the fact the language

generally does not require the programmer to perform memory management.