javascript - Why does my anonymous function not have the context of the current object in this example? -


when run sample code in google chrome, intended behavior--loading image within placeholder image tag on current page--does not occur. checked value of currpic when showpic() called, , "undefined." know if change parameter showpic 'anchors[i]' 'this', work, trying understand why so. 

function showpic(currpic) {     var srcloc = currpic.getattribute("href");     var placeholder = document.getelementbyid("placeholder");     placeholder.setattribute("src", srcloc);     var imglabel = document.getelementbyid("imglabel");     var currlinktitle = currpic.getattribute("title");     imglabel.firstchild.nodevalue = currlinktitle; }  function preparegallery() {     if(!(document.getelementsbytagname && document.getelementbyid)) return false;      var imggallery = document.getelementbyid("imagegallery");      if(imggallery) {         var anchors = imggallery.getelementsbytagname("a");         var i;         for(i = 0; < anchors.length; i++) {             anchors[i].onclick = function() {                 showpic(anchors[i]);                 return false;         }           }     } }

inside anonymous function, anchors[i] provides runtime reference. @ time click occurs, anchors[i] no longer exists. while existed @ time assignment made, falls out of scope @ time of click (since it's array reference). however, using this provides solid reference immediate object available @ time of click.

more succinctly, anchors[i] reference position in array (which leaves scope once loop exits). this reference dom element itself.


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