Prevent ajax call from firing twice

An alternative to disabling the button would be to use the .one() method and re-bind the event handler after callback:

var clickHandler = function(e){
    $.ajax({
      url:  url,
      type: 'POST',
      async: true,
      dataType: 'json',
      enctype: 'multipart/form-data',
      cache: false,
      success: function(data){
        $('#button1').one('click', clickHandler);
      },
      error: function(){}
    });
    e.stopImmediatePropagation();
    return false;
}

$('#button1').one('click', clickHandler);