jQuery provides an extremely versatile DOM query mechanism. If you’re wondering what’s happening under the covers, and if there are less- and more-performant ways to formulate your query . . . the answer is YES. In many cases you can help jQuery by specifying a tag name, i.e.:
is faster than:
. . . with the difference being that the query engine can narrow by tag name first. It’s smart like that.
So, you shoud be in the habit of specifying a tag name. The only exception: getting by ID. If you’re getting by ID, do not include a tag name, or anything else besides the ID selector.
Note that the second example here (with the class selector only) is perfectly valid, and if you need to query for multiple element types, by all means go ahead — jQuery will still return the correct results.