Focus on creating 'working' JavaScript, along the way encourage proper formatting/syntax, labeling, etc as you go. Useful type-in in examples are great.
As an example I needed to make a field input aid for a project, this one would be an alternative to a [YYYYMM] text entry, where they click on the tool button and are presented in a popup (ala date/time picker) with a range of months around the current date (or range specified in the calling code) where the user could quickly click the appropriate textual month/year and it fills in the form... also pulls the current field data into the script.
Examining date time picker code - I got it figured out. The books I've bought/checked don't seem to cover (or cover well enough to recognize it) what I was looking for. So an annotated cookbook approach I feel would be a good and mix in the style/management along with it.
I'm sure others working mainly on the backend code wanting some more front end support code would be interested in such a book as I would.