javascript - getElementsByTagName("*") always updated? -

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i have made code:

var foo=document.createelement("div");  var childs=foo.getelementsbytagname("*");  console.log(childs.length);//0 ok  var a=document.createelement("a");  foo.appendchild(a);  console.log(childs.length);//1 wtf?

a fiddle: http://jsfiddle.net/rl54z/3/

i don't have write childs=foo.getelementsbytagname("*"); between fifth , sixth line childs.length updated.

how can be?

most lists of nodes in dom (e.g. returned getelementsby*, queryselectorall, , node.childnodes) not simple arrays rather nodelist objects. nodelist objects "live", in changes document automatically propagated nodelist object. (an exception result queryselectorall, not live!)

so can see in example, if retrieve nodelist of a elements, add a element document, a appear in nodelist object.

this why unsafe iterate through nodelist while making changes document @ same time. e.g., code behave in surprising ways:

var nodelista = document.getelementsbytagname('a');  (var i=0; i<nodelista.length; ++i) {    // unsafe: don't this!    nodelista[i].parentnode.removechild(nodelista[i]); }

what happen end skipping elements! either iterate backwards end of nodelist, or copy nodelist plain array (which not update) , work that.

read more nodelists @ mozilla mdc site.


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