Speaking to the reason he's writing this, if a vacancy is asking for jQuery, it probably means they're using jQuery (obvious). The author mentioned other stuff you can use to get specific jQuery functionality, but I think it should be emphasized that if you just got a job where jQuery was a requirement, you should look into implementing alternatives ASAP. One good recommendation I have is to use MinifiedJS:
It has a lot of the things you would need jQuery to do and is tiny and cross-browser. If pure JS isn't an option, MinifiedJS is the next best thing. For now, most web developers should still learn jQuery, but they should transition stuff off jQuery so one day it's not as widespread a requirement.