Jquery

TIP

jquery 的知识整理。
Jquery

.serialize()

参考链接:serialize

WARNING

勾选框需要选中的时候，才会获取值进行传递：
For a form element's value to be included in the serialized string,
the element must have a name attribute. Values from checkboxes and radio buttons
(inputs of type "radio" or "checkbox") are included only if they are checked.
Data from file select elements is not serialized.

.val()

1. when called on an empty collection, it returns undefined.

   当没有匹配到对应元素的时候比如:$('#kkk').val()

2. When the first element in the collection is a select-multiple (i.e., a select element with the multiple attribute set), .val() returns an array containing the value of each selected option. As of jQuery 3.0, if no options are selected, it returns an empty array; prior to jQuery 3.0, it returns null.

   当前使用的是jq1.12.x所以，如果是下拉框选择的数据的话，无数据--option的直接返回：null