javascript - Constantly check the length of an element and perform an action if it is ever 1 -


i have element on page monitoring. if @ time length equal 1, means exists on page (the user has logged out) , want prompt them popup login.

so @ moment have this:

function loginnotice() {     //do prompt } keepalive();  function keepalive() {     if($('.username_field').length == 1){         loginuser();     }     try {         settimeout(function(){keepalive();}, 10000);     } catch (ex){     } }

i don't think efficient. checks every , runs prompt if need be. thing page may load , length may 1 already, or may 0. don't know @ given time can't on change.

is there way can more efficiently?

you can use mutation observer on parent/ancestor node instead, watching changes subtree and/or childlist.

var ancestor = $("...closest ancestor doesn't change..."); // worst case, $('body') var ob = new mutationobserver(function() {     if($('.username_field').length == 1){         loginuser();     } }); ob.observe(ancestor[0], {     subtree: true,   // need...     childlist: true  // ...one of these or other });

having said that, though, doing dom query every 10 seconds isn't problem @ all; if don't need faster reactions that, current solution fine.


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