// 将form序列化为key1=value1&key2=value2这样的个数，在ajax提交form表单时很有用。

function serialize(form) {
  var parts = [],
    field = null, i,
    len,
    j, optLen, option, optValue;
  for (i = 0, len = form.elements.length; i < len; i++) {
    field = form.elements[i];
    switch (field.type) {
      case "select-one":
      case "select-multiple":
        if (field.name.length) {
          for (j = 0, optLen = field.options.length; j < optLen; j++) {
            option = field.options[j];
            if (option.selected) {
              optValue = "";
              if (option.hasAttribute) {
                optValue = (option.hasAttribute("value") ?
                  option.value : option.text);
              } else {
                optValue = (option.attributes["value"].specified ?
                  option.value : option.text);
              }
              parts.push(encodeURIComponent(field.name) + "=" +
                encodeURIComponent(optValue));
            }
          }
        }
        break;
      case undefined:      //字段集
      case "file":         //文件输入
      case "submit":       //提交按钮
      case "reset":        //重置按钮
      case "button":       //自定义按钮
        break;
      case "radio":        //单选按钮
      case "checkbox":     //复选框
        if (!field.checked) {
          break;
        }

      default:
        //不包含没有名字的表单字段 
        if (field.name.length) {
          parts.push(encodeURIComponent(field.name) + "=" + encodeURIComponent(field.value));
        }
    }
  }
  return parts.join("&");
}