前端：用on对动态生成的元素绑定事件

由于一般的事件注册仅对已经存在的元素有效，所以对于未来生成的元素注册事件不能用一般的方式。

在jquery1.8及以前可以用live方法，1.9之后用on，但并不是简单的替换，因为参数不同。

.live(events, function)

should map to:

.on(eventType, selector, function)

The selector is very important! If you do not need to use this for any reason, set it to null.

Migration Example 1:

before:

$('#mainmenu a').live('click', function)

after, you move the child element (a) to the .on() selector:

$('#mainmenu').on('click', 'a', function)

Migration Example 2:

before:

$('.myButton').live('click', function)

after, you move the element (.myButton) to the .on()selector, and find the nearest parent element (preferably with an ID):

$('#parentElement').on('click', '.myButton', function)

If you do not know what to put as the parent, body always works:

$('body').on('click', '.myButton', function)