In this book by Wesley Hales written on 2012, expect to find a good description about why there are so many web applications with Javascript and different  approaches on how to do it.

It starts with a quick review on why we are moving code from server to client. It covers mobile web and the main points on developing solutions for these devices: what to support, look and feel, interactions and different frameworks that we can use.

You can applied the knowledge about mobile web that you can find in this book to develop mobile apps multiplatforms because they share very similar concepts.

About HTML5, websockets, geolocation, webstorage and webworkers are the main topics.

All the topics in this books are covered not very deeply, so think on this book like an introduction to these concepts (it´s only 150 pages) and not like your reference guide for developing web apps.

I think that it´s a good option if you want to have a global view and decide on what to include or not on your next mobile web application. What technology to use, what browsers you can support, how to debug them, what frameworks you can use and so.

I like when it introduces a technology (HTML5) and tells you what browsers you can use with it. Maybe you can discover that it´s too early for some technologies or that if you develope a webapp, you have to choose between latest technology or compability. But what it´s clear about this technology  is that you must keep an eye on it.