Question

I am trying to get the ID of an element bound with a jQuery delegate() function. I want to pass the element’s ID to another function. The ID returned is always “undefined” and I’m not sure why. Here is my code:

$(document).ready(function() {
  var timeout = undefined;
  $('body').delegate(
    '#tab-form input[type="text"]',
    'keypress',
    function(){
      if(timeout != undefined) {
        clearTimeout(timeout);
      }
      timeout = setTimeout(function() {
        timeout = undefined;
        alert($(this).attr('id'));
      }, 500);
    }
  );
});

And my markup:

<form id="tab-form">
  <input type="text" value="" id="Tab_name" name="Tab[name]">
  <input type="text" value="" id="Tab_text" name="Tab[text]">
</form>

Making a keypress in the text input pops up a JS alert that says “undefined”, instead of “Tab_name” or “Tab_text” like I imagined it would.

My initial Googling around leads me to believe that the reason for the attr(‘id’) being undefined is that “this” is not actually a single DOM element, but is an array of the elements that delegate() is attached to. I have not been able to figure out how to access the current bound element’s DOM object in the jQuery object array.

Any help is much appreciated!

Answer 1

The context is window because window owns setTimeout. Just cache it:

$(document).ready(function() {
  var timeout = undefined;
  $('body').delegate(
    '#tab-form input[type="text"]',
    'keypress',
    function(){
      var el = this;
      if(timeout != undefined) {
        clearTimeout(timeout);
      }
      timeout = setTimeout(function() {
        timeout = undefined;
        alert($(el).attr('id'));
      }, 500);
    }
  );
});