.keydown()
Bind an event handler to the "keydown" event, or trigger that event on an element.
分类：Keyboard Events
keydown event
为 "keydown" 事件绑定一个处理函数，或者触发元素上的 "keydown" 事件。
.keypress()
Bind an event handler to the "keypress" event, or trigger that event on an element.
keypress event
为 "keypress" 事件绑定一个处理函数，或者触发元素上的 "keypress" 事件。
.keyup()
Bind an event handler to the "keyup" event, or trigger that event on an element.
keyup event
为 "keyup" 事件绑定一个处理函数，或者触发元素上的 "keyup" 事件。