Question

I’m trying to hide tr’s within a html table if the inputs inside them match a certain criteria.
The criteria is defined by a dropdown’s selected value.
I’m doing it like so:

$(function () {

  $('body').find('#p_Selection').live('change', function () {

    var type = $('body').find('#p_Selection').attr('value');
    var tableRow = $('.goods').find('.detail-child tr');

    tableRow.each(function (index) {

      var Record_LidExpected = $('input[id$=Record[' + index + ']_LidExpected]').attr('value');
      var Record_LidObtained = $('input[id$=Record[' + index + ']_LidObtained]').attr('value');
      var Record_QuantityExpected = $('input[id$=Record[' + index + ']_QuantityExpected]').attr('value');
      var Record_QuantityObtained = $('input[id$=Record[' + index + ']_QuantityObtained]').attr('value');

      if (type == "1") {

        if (Record_LidExpected != Record_LidObtained) {
          $(this).hide();
        }
        else {
          if (Record_QuantityExpected != Record_QuantityObtained) {
            $(this).hide();
          }
        }
      }
      else {
        if (type == "2") {
          if (Record_LidExpected == Record_LidObtained) {
            $(this).hide();
          }
          else {
            if (Record_QuantityExpected == Record_QuantityObtained) {
              $(this).hide();
            }
          }
        }
        else {
          if (type == "0") {
            $(this).show();
          }
        }
      }
    });
  });
});​

This script became extremely slow inside my aspx page and it just won’t complete because it is too heavy.
Any suggestions on how to make it faster?

Answer 1

The key points of preformance optimization

• do few selects (don’t select everything onchange)
• save selections that won’t change
• be as specific as possible when you select elements

Bonus: learn to use else if because your branches become clearer.

Here is the code:

$(function () {

  // pre-select things that won't change
  var $sel = $('#p_Selection'); 
  var tableRow = $('.goods .detail-child tr');

  //
  // ONCHANGE EVENT 
  // keep in mind that everything in it will be very costly
  //
  $sel.live('change', function () {

    var type = $sel.attr('value');

    tableRow.each(function (index) {

      // this just makes the code shorter
      var record = '#Record'+index;

      // simple ID selector is enough, since its unique
      var Record_LidExpected =  $(record+'_LidExpected').attr('value');
      var Record_LidObtained =  $(record+'_LidObtained').attr('value');
      var Record_QuantityExpected = $(record+'_QuantityExpected').attr('value');
      var Record_QuantityObtained = $(record+'_QuantityObtained').attr('value');

      if (type == "1") {
        if (Record_LidExpected != Record_LidObtained) {
          $(this).hide();
        } else if (Record_QuantityExpected != Record_QuantityObtained) {
          $(this).hide();
        }
      } else if (type == "2") {
        if (Record_LidExpected == Record_LidObtained) {
          $(this).hide();
        } else if (Record_QuantityExpected == Record_QuantityObtained) {
          $(this).hide();
        }
      } else if (type == "0") {
        $(this).show();
      }
    });
  });
});