[S4M]

Unlike the other commenters, I wouldn't suggest any book yet. Instead, start playing with the language. Take your browser, bring on the javascript console (on Firefox it's ctrl-shift-K, on Chrome it's ctrl-shit-j), and start entering some instructions. Add some numbers, concatenate some strings, do a for loop, create and call a function...

Then learn how to run a script from the browser (create a html file and inside write <script src="my_code.js"></script>, and put my_code.js in the same repertory as the html page, and finally open the it with the browser).

Then, play around, learn how javascript can interactively change a page, etc.