此处的示例: http://jsfiddle.net/jkeyes/dYbfY/2/

$("#text_box_url").blur(function() {
  var input = $(this);
  var val = input.val();
  if (val && !val.match(/^http([s]?):\/\/.*/)) {
    input.val('http://' + val);
  }
});

更新一种解决方案，该解决方案保留了所有值，并且保留了不变的方案: http://jsfiddle.net/jkeyes/c6akr9y2/

Update a solution that leaves all values with a scheme untouched: http://jsfiddle.net/jkeyes/c6akr9y2/