A good collection of "How to" article using Javascript object model (JSOM) on MSDN. It will be useful in developing apps in SharePoint 2013.
- How to: Work with Websites Using JavaScript
- How to: Retrieve List Items Using JavaScript
- How to: Create, Update, and Delete List Items Using JavaScript
- How to: Retrieve Lists Using JavaScript
- How to: Create, Update, and Delete Lists Using JavaScript
- How to: Work with Users and Groups Using JavaScript
- How to: Work with Roles Using JavaScript
- How to: Break Role Assignment Inheritance Using JavaScript
- How to: Add and Modify User Custom Actions Using JavaScript
- How to: Work with Web Parts on a Page Using JavaScript
