Re: Reference var in (function(){})()

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From	Thomas 'PointedEars' Lahn <PointedEars@web.de>
Newsgroups	comp.lang.javascript
Subject	Re: Reference var in (function(){})()
Date	Wed, 02 Aug 2017 11:33:09 +0200
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Thomas 'PointedEars' Lahn wrote:

> Andrew Poulos wrote:
>> I'd like to reference them in a for loop e.g.
>> 
>> for (i = 0; i < len; i++) {
>>    eval("opt" + i) = ...
>> }
>> 
>> but how can I do it without using eval?
> 
> You cannot.  Therefore, use an Array instance –
> 
>   […]
> 
> – or an Object instance –
> 
>   var con = (function () {
>     /* “opt” then refers to an object that does not inherit properties */
>     var opt = Object.assign(Object.create(null), {
>       0: {},
>       1: {},
>       2: {},
>       3: {}
>       // , ...
>     });
>  
>     function x ()
>     {
>       for (var i = 0; i < len; ++i)
>       {
>         // opt[i] = ...
>       }
>     }
> 
>     // x(…)
>   })();
> 
> – instead.

Note that, with exceptions, the better approach is not to rely on the scope 
chain, but to pass a reference to the pertaining object:
  
  var con = (function () {
    /* “opt” then refers to an object that does not inherit properties */
    var opt = Object.assign(Object.create(null), {
      0: {},
      1: {},
      2: {},
      3: {}
      // , ...
    });
 
    function x (obj)
    {
      for (var i = 0; i < len; ++i)
      {
        // obj[i] = ...
      }
    }

    // x(opt)
  })();

This way, not only is the effective scope chain shorter, which is faster, 
but also the function code can be moved elsewhere for reuse without 
necessarily modifying it further.  For example,

  function x (obj)
  {
    for (var i = 0; i < len; ++i)
    {
      // obj[i] = ...
    }
  }

  var con = (function () {
    /* “opt” then refers to an object that does not inherit properties */
    var opt = Object.assign(Object.create(null), {
      0: {},
      1: {},
      2: {},
      3: {}
      // , ...
    });
 
    // x(opt)
  })();

works just as well.

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PointedEars
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Reference var in (function(){})() Andrew Poulos <ap_prog@hotmail.com> - 2017-08-01 12:09 +1000
  Re: Reference var in (function(){})() "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2017-08-01 09:39 +0200
  Re: Reference var in (function(){})() Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-08-01 12:40 +0200
    Re: Reference var in (function(){})() Andrew Poulos <ap_prog@hotmail.com> - 2017-08-02 14:06 +1000
      Re: Reference var in (function(){})() Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-08-02 11:38 +0200
    Re: Reference var in (function(){})() Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-08-02 11:33 +0200

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