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Posted by Onideus Mad Hatter on 07/08/05 21:38
On Fri, 08 Jul 2005 13:17:49 GMT, Michael Winter
<m.winter@blueyonder.co.uk> wrote:
>On 08/07/2005 12:05, ^reaper^ wrote:
>
>[snip]
>
>> Or, for example, say you want to reference a document object that
>> contains a variable component, you can do something like this:
>>
>> eval('document.all.'+name+'.style');
>
>Even then, it's not necessary:
>
> document.all[name].style
>
>The eval function is best left for /arbitrary/ strings that need to be
>evaluated as code. However, it is very rare that one will ever have such
>a need.
>
>The only use I've found so far is for emulating the
>Function.prototype.call or apply methods in (mainly) earlier IE
>versions. Unlike the dynamic construction of property names, there is no
>other way of building an argument list at run-time without the use of
>the apply method.
>
> var global = this;
>
> if('function' != typeof Function.prototype.apply) {
> Function.prototype.apply = function(o, a) {
> var x = [],
> p = ' $apply',
> r, u;
>
> if(null == o) {o = global;}
> while('undefined' != typeof o[p]) {p += p;}
> o[p] = this;
>
> if(a && (Array == a.constructor) && a.length) {
> for(var i = 0, n = a.length; i < n; ++i) {x[i] = i;}
> r = eval('o[p](a[' + x.join('],a[') + ']);');
> } else {
> r = o[p]();
> }
> o[p] = u;
>
> return r;
> };
> }
>
>Still, even that has a slight problem. Though IE will set the this
>operator value correctly for a null or undefined first argument, this
>value will not compare properly to the global object.
>
>All that said, given the fact that one usually knows how many arguments
>will be needed in a call to one of these methods, this form of generic
>emulation is rarely needed.
>
>I have seen other interesting uses for the eval function, but even they
>weren't really necessary.
It gives me a warm fuzzy feeling inside to know that I've found a
purpose for the lonely little eval function. It may not be truly
functional, but it makes it so I can read my code eaiser...and really,
that's all that matters.
--
Onideus Mad Hatter
mhm ¹ x ¹
http://www.backwater-productions.net
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