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Message-ID: <8927386.SEqChMirdb@PointedEars.de>
From: Thomas 'PointedEars' Lahn <PointedEars@web.de>
Reply-To: Thomas 'PointedEars' Lahn <cljs@PointedEars.de>
Organization: PointedEars Software (PES)
Date: Sat, 22 Oct 2011 14:35:56 +0200
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Subject: Re: Get value of named object
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.javascript:7617

Swifty wrote:

> If I have the name of an object in a variable,

That is _not_ the name of an object (objects have _identity_, not name).  It 
is a possible reference path of a property (a property accessor) which value 
refers to that object.

> how would I go about getting the value of that object?
> 
> Example:
> varname = 'navigator.appName';
> 
> How would I get the value of navigator.appName ?

eval(varname).  But you really don't want to do that.
 
> See http://swiftys.org.uk/jsvars.html for my first, faltering attempt.
> 
> The idea is to replace the multiple "document.write" lines with the
> simpler "show()" calls.

(Your current show() would still cause document.write() to be called 
consecutively, which is a bad idea.)

Consider this:

  var properties = [
    ["navigator", "appCodeName"],
    ["screen", "availHeight", "availWidth"],
    ["window", "closed", "history", "innerHeight", "innerWidth",
     ["location", "hostname", "pathname"], "outerHeight", "outerWidth"]
  ];

Then iterate recursively over this data structure, starting with

  _global[properties[i][0]]

where `_global' is a reference to the ECMAScript global object (`this' in 
the global execution context) and `i' is the iterator variable.  Complete 
and improve this:

  var out = [];

  for (var i = 0, len = properties.length; i < len; ++i)
  {
    var properties2 = properties[i];
    var base = properties2[0];
    for (var j = 1, len2 = properties2.length; j < len2; ++j)
    {
      var property = properties2[j];
      out.push(
        "…" + base + "." + property + "…" + _global[base][property] + "…");
    }
  }

  document.write("…" + out.join("…") + "…");

You may use Object instances as well if you do not care about order or 
if you iterate over property values in an order that you define.  In any 
case, you have to take care of inherited and special properties, then.

Since you are dealing with host objects here, you have to be extra careful 
with "unknown"-type properties and to catch any exceptions a property access 
can throw.


PointedEars
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