Some Javascript file handling links:
Writing files:
Eli Grey: Article describing his library FileSave.js
Demo 1: FileSaver.js demo of saving text from a HTML text area
Demo 2: FileSaver.js demo of saving a string in a blob
Github: Source for FileSaver.js
Reading the contents of files:
Treehouse: Several examples of opening files and displaying the contents in a web page
HTML5 Rocks: Multiple examples of opening files
NCZOnline: Code-only examples, no live demos