JavaScript control flow constructs: browser-specific or inherent JS

I put together a little function rangein JS. I tested it in Chrome 19, FF, and IE (7-9) and it works well. The question I have is related to the operator while.

function range(from,to,step)
{
    'use strict';
    var sCode,eCode,result;
    result = [];
    step = (!step || isNaN(step) || step === 0 ? 1 : step);
    sCode = (''+from).charCodeAt(0);
    eCode = (''+to).charCodeAt(0);
    step *= (sCode > eCode && step > 0 ? -1 : 1);
    do
    {
        if (String.fromCharCode(sCode))
        {
            result.push(String.fromCharCode(sCode));
        }
    }while((step > 0 && eCode >= (sCode+=step)) || (step < 0 && eCode <= (sCode+=step)));
    return result;
}

I remember reading a question for some time about how JS handles control flow constructors and logical operators. I think this has something to do with checking if the object had a specific method, and if so, using its return value ( if (event.returnValue && e.returnValue === true)kind of things).
I can no longer find this question, here is what I wanted to know:

while((step > 0 && eCode >= (sCode+=step)) || (step < 0 && eCode <= (sCode+=step)));

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