function serialize(form){
 var params = [];
 var eles = form.elements;
 
 for (var i = 0;i<ele.length;i++){
  let field = ele[i];
  switch(field.type){
   case "file": 
   case "submit":
   case "reset": 
   case "button":
    break;
   case "radio":
   case "checkbox":
    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("&");
}