Looping over Array

[schephais]

Appending methods to the Object or Array objects breaks "for...in" loop use:

Object.prototype.myMethod = function ()
{
   return "my result";
}

var myArray = new Array('red','green','blue','pink');
for(myKey in myArray)
   alert(myKey);

I expected the above code to return the array keys for the myArray array. However, because I used the Object prototype to append a method to Object, the "for...in" loop will begin acting unpredictably. I could patch this up to catch for the 'myMethod' key, but this seems rather cowboy (what if I want to further extend the Object model?)

A Google search for solutions to this revealed the following quip from someone's blog:
"...using the 'in' operator on arrays is incorrect."
He didn't, however, offer any alternative.

Does anyone know of a more reliable method of looping over arrays?

Edit:
Charles pointed out that in the above example, the array keys will all be numeric so I can use a regular for or while loop to loop over all the elements in the array. However, what about associative arrays? Also, am I making a mistake in my use of the prototype - is there another method of appending methods to objects without also appending them as properties?

SOLVED
I have now solved this problem. Please see my comment below ("SOLUTION...") for details.

Many thanks.

[vwphillips]

well this bit works

<script language="JavaScript" type="text/javascript">
<!--
var myArray = new Array('red','green','blue','pink');
for(myKey in myArray){
   alert(myKey);
}
//-->
</script>

but what are you trying to do?

[Charles]

Try:

var e, i = 0
while (e = array[i++]) {}

[schephais]

Thanks! This works well for numeric arrays, but what about associative arrays?

[schephais]

JavaScript allows programmers to append methods and properties to already initialized objects. In the above example, I've appended the (rather useless) function 'myMethod' to the Object object - the root object for all objects in JavaScript - with the intent of using it as a method.

Another of JavaScript's features is the ability to access object properties as array elements. So if 'myArray' is an array then myArray['myMethod'] returns the code used in the myMethod method. This is why the for...in loop doesn't work in the full example (when you incldude the myMethod declaration).

[schephais]

SOLUTION

I discovered the following solution to the above problem:

Object.prototype.myMethod = function ()
{
   return "my result";
}

var myArray = new Array('red','green','blue','pink');
for(myKey in myArray)
   if(myArray.propertyIsEnumerable(myKey))
      alert(myKey);

As you can see, this uses the 'propertyIsEnumerable' Object method to check the each property of the array object that meets the 'in' operator. I haven't tested this in JScript, but it works in JavaScript 1.5 and is supported by ECMAScript 3.

Thanks for your help, everyone.