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Does this kind of value setting work in Javascript?

I'm trying to create code that requires the least number of bytes and that works for all browsers including IE 7.
In this example, the program calls dosomething('x1') and dosomething('x2').
If I have code like this:
var items,item,index,count;
items=Array('x1','x2');
count=items.length;
for (index=0;index<count;index++){
item=items[index];
dosomething(item);
}
Could I reduce it to this and have it still function exactly the same in all browsers:
var a=Array('x1','x2'),c=a.length,i;
for (i=0;i<c;i++){
f(a[i]);
}
I understand I changed the variable names and calling function name but my goal is to use the least number of bytes possible in the code to make the code execute.
I'm just not sure if declaring a variable equal to a property of a value from a previous variable in the same list of declarations would actually return correct results.
In other words, does var a=Array('x1','x2'),c=a.length... work, or do I have to specifically do var a=Array('x1','x2');var c=a.length; to make it work in all browsers including IE 7?

This is what the Google Closure Compiler service returned:
var a,b,c,d;a=["x1","x2"];d=a.length;for(c=0​;c<d;c++)b=a[c],dosomething(b);
You can find many different Javascript compressors online to automate the process you are hand coding now. Yet, it's always good to understand how they work as it helps to write code that is better compressed.
As for IE, you can test your code by changing the emulations settings in the IE debugger panel. Just press F12, click the Emulation tab, and adjust the document mode to 7 (IE7).
Hope this is enough to get you started in the right direction.

You can use Array.map from IE 9
var items = Array('x1','x2');
items.map(dosomething(item));

Jquery issues on older versions of IE

I have the following statement in document.ready function:
if($("sidebar ").html().trim().length == 0)
{
$("sidebar").append("<p> The sides..</p>");
};
It works fine in IE 9 but as soon as I select IE 8 (browser and document standard), the script stops working and gives the following error:
SCRIPT5007: Unable to get value of the property 'trim': object is null or undefined
application-e51c9eee7d22e9644481115dc1fedd5f.js, line 7 character 17578
I looked at the .js in debug mode and see that my statement above is transformed to:
$("sidebar ").html().trim().length==0&&$("sidebar").append("<p> The sides..</p>")
How do I prevent this error? Please note that I do see that the node is present in the rendered page.
I thought that maybe just having reference to shiv5.html may not be sufficient to take care of the IE idiosyncrasies. So, I have added modernizr.js via sprockets and I have added class="no-js" in my layout. Still no luck in IE <9.
What am I missing? What else can I do to get the favor of Microsoft overlords?

According to MDN, trim isn't available in IE < 9.
You could use $.trim instead:
if($.trim($("sidebar ").html()).length == 0)
{
$("sidebar").append("<p> The sides..</p>");
} // <-- Don't want a semicolon here.
The MDN article lists an alternative if you don't want to find all the instances of trim and correct them. You could use the following to create .trim if it's not natively available:
if(!String.prototype.trim) {
String.prototype.trim = function () {
return this.replace(/^\s+|\s+$/g,'');
};
}

Check out this thread. After a quick search it seems that many people are experiencing issues with trim.

javascript options.length = 0 not working in IE9

I have a page that sets the length of a select list to 0 before it adds new options. This worked fine in all browsers until IE9. In IE9 I get the error: DOM Exception: NOT_FOUND_ERR (8). This is all I'm trying to do:
var typebox = document.sForm.ePosition;
typebox.options.length = 0;
Works fine in compatibility mode.

Try executing each piece in your console, and see where your exception is:
document.sForm
document.sForm.ePosition
document.sForm.ePosition.options
document.sForm.ePosition.options.length
I tried setting the length of options to 0, and was pretty surprised that it worked (in Chrome). Array.length should be a read-only property, in my opinion. I would use DOM code to remove the elements, something like this:
while (element.hasChildNodes()) {
element.removeChild(element.firstChild);
}

I was just struck by the same issue and found a convenient solution for those of us using jQuery:
$(selectObject).empty();
I've tested this in IE 7-9, FF 10.0 and Chrome 18 using jQuery 1.4.4.

Question was in pure javascript, please supply first a pure javascript reply. The users could not be interested in jquery since many embedded solutions can't use jquery.

IE Javascript error "Object doesn't support this property or method" within jQuery

For some reason, I am getting the following Javascript error in Internet Explorer 8 on line 3156 of jquery.js (version 1.4.3, non-compressed version): Object doesn't support this property or method. No error occurs in Firefox and Google Chrome.
This is the line the error occurs on:
if ( (match = Expr.leftMatch[ type ].exec( expr )) != null && match[2] ) {
Investigation (console.log(Expr.leftMatch[type])) produces the following interesting result: In Google Chrome, it outputs
/(^(?:.|\r|\n)*?):((?:[\w\u00c0-\uFFFF\-]|\\.)+)(?:\((['"]?)((?:\([^\)]+\)|[^\(\)]*)+)\3\))?(?![^\[]*\])(?![^\(]*\))/
However in Internet Explorer this is the output:
function() {
var p = this;
do p = p.previousSibling;
while (p && p.nodeType != 1);
return p;
}
On which exec cannot be called (it is undefined). The quoted function is not present within jquery.js. Does anyone have any clue why this happens, or what I can do to solve it?
I have, unfortunately, not yet been able to create a simple script to reproduce the problem, although I did find this post of someone having the same problem, but it does not offer a solution (the last post suggests the page should be run in Standards Mode, but mine already is).

As it turns out, I managed to figure it out by myself after several painful hours. It appears the Sizzle selector engine breaks in this unexpected way (and only in Internet Explorer), if you have defined Object.prototype.previousObject elsewhere.
Removing that declaration, or renaming previousObject to something else fixes the problem.
The funny thing is, I even put that code there myself (the Object.prototype.previousObject = [the function in my question]), but I did not recognize the code.
Well, that's another day full of development potential wasted.

I have discovered the same behaviour occurs if you attempt to add a method called "inherited" to the Object.prototype, ie Object.prototype.inherited = <some func>
It affects IE6, 7 & 8 but seems to be fixed in IE9 (beta)

May be to late to respond but I had the same problem and solved with selecting elements with plain java script rather then jquery!
var div = document.getElementById("myDiv");
var rect = div.getBoundingClientRect();
This works some how!

JQuery issue (major) with IE - all versions

This only happens with IE (all versions), on line 1120 in
jquery-1.2.6.js I get the following error:
Line 1120:
Invalid Property Value
The line in the js file is the following:
elem[name] = value;
It is inside attr: function( elem, name, value )
Does anybody have a problem similar to this?

If this is also you, it sounds like you're trying to change the CSS of the element rather than give it an attribute.
If that is the case then try this instead;
jQuery.css('color', 'inherit');

This error can also occur if you call jQuery.css with an invalid attribute value, such as:
$('div.foo').css('padding-left', 'NaNpx');

The problem is IE-only because you are probably trying to set something like "min-height" which exists in (a proper CSS implenting) browser like Firefox, but not in a (demon spawned fiend of a) browser like Internet Explorer. I ran in to the same issue using jQuery's own dialog UI function.
I was a huge proponent of jQuery before this, but this has really put some egg on its face.