quick jquery check for repeated / duplicate ids in DOM

Coworker suggested this console-code proof that ids were being duplicated:
  $('[id]').each(function(){
var ids = $('[id="'+this.id+'"]');
if(ids.length>1 && ids[0]==this)
console.warn('Multiple IDs #'+this.id);
});
If I was less lazy I'd cook up the non-jQuery version.