jQuery中.find()跟.filter()的区别
The jQuery .find() method can be used to create a new set of elements based on context
of the current set of DOM elements and their children elements. People often confuse
the use of the .filter() method and .find() method. The easiest way to remember
the difference is to keep in mind that .find() will operate/select the children of the
current set while .filter() will only operate on the current set of elements. In other
words, if you want to change the current wrapper set by using it as a context to further
select the children of the elements selected, use .find(). If you only want to filter the
current wrapped set and get a new subset of the current DOM elements in the set only,
use .filter(). To boil this down even more, find() returns children elements, while
filter() only filters what is in the current wrapper set.