Find something that bothers you about a site you use a lot, and build a Chrome extension to fix it. (Hiding the Moments tab on Twitter is a good start.)
As said before you should try the projects on Codecademy in the Javascript track.
Hey,
Try the JavaScript track on Codecademy. First they make you go through simple tutorials then ask you to build things. I remember building a Blackjack bot in their earlier days.
Prashant Abhishek
Co-founder at AltCampus
There are some nice answers by folks here-
Suggest simple libraries to read source code for learning JS
How can I learn JavaScript in 24 hours?
However specifically for 'learning by projects'-
Make a simple page where you change color of background etc on clicks
Make a calculator
Make a Todo app (store data on localstorage, use simple javascript or jquery)
Make a simple chrome extension to customize your homepage (or anything)
Make a small game ( Eloquent JavaScript walks through making a game)
Make a small Express based app (maybe your dynamic personal website)
Finally choose any of these new JS frameworks and make whatever you wish.
I will recommend that you use Eloquent JavaScript as guide for learning theory part while learning it.
Good luck, build something and show us on Hashnode. :)