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From: Thomas 'PointedEars' Lahn <PointedEars@web.de>
Newsgroups: comp.lang.javascript
Subject: Re: removeeventlistener
Date: Sat, 28 Oct 2017 20:00:26 +0200
Organization: PointedEars Software (PES)
Lines: 64
Message-ID: <19619642.EfDdHjke4D@PointedEars.de>
References: <e4ednXbpPvgtunnEnZ2dnUU7-bXNnZ2d@westnet.com.au> <2412105.mvXUDI8C0e@PointedEars.de> <1746259.PYKUYFuaPT@PointedEars.de>
Reply-To: Thomas 'PointedEars' Lahn <cljs@PointedEars.de>
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Xref: csiph.com comp.lang.javascript:34223

Thomas 'PointedEars' Lahn wrote:

>   var elementOvers = [];
> 
>   function setOver (elements)
>   {
>     /*
>      * NOTE:
>      * You may want to use ES 5 [].forEach.apply(elements, …) or
>      * ES 6 “for … of” on [].slice.call(elements) instead.
>      *
>      * In loops, cache the value of the “length” property unless you
>      * expect its value to change and want to handle that.
>      */
>     for (var i = 0, len = elements.length; i < len; ++i)
>     {
>       /* NOTE:
>        * You can still return the function reference instead.
>        * Just keep in mind that in the way it is used here,
>        * there is a closure over “i”.
>        *
>        * Consider using CSS “:hover” selectors based on class selectors
>        * instead of setting style properties here.
>        */
>       var elementOver = elementOvers[i] = function () {
>         this.style...
>       };

Supplemental:

If all listeners for the same event implement the same algorithm, you only 
need to define *one* such function such that it can be shared across 
function execution contexts –

  var elementOver = function () {
    // …
  };

–, and re-use the reference to it:

  function (…)
  {
    for (…)
    {
      elements[i].addEventListener("mouseover", elementOver, false);
    }
  }

  …

  function (…)
  {
    for (…)
    {
      elements[i].removeEventListener("mouseover", elementOver);
    }
  }

That would be much more efficient then.
 
-- 
PointedEars
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