IndexedDB is an object database, not a relational database, and it is much simpler than databases that support SQL queries. It is more powerful, efficient, and robust than the key/value storage provided by the Web Storage API, however.

A key path is defined as a value that tells the database how to extract an object’s key from the object.

Data stored through localStorage is permanent: it does not expire and remains stored on the user’s computer until a web app deletes it or the user asks the browser (through some browser-specific UI) to delete it.

To retrieve a value, pass the name to getItem().

To store a value, pass the name and value to setItem().

The various forms of client-side storage are web databases, filesystem API, Offline web applications and cookies.

HTML5 defines an “Offline Web Applications” API that allows the caching of web pages and their associated resources (scripts, CSS files, images, and so on). This is client-side storage for web applications themselves rather than just their data, and it allows web apps to install themselves so that they are available even when there is no connection to the Internet.

Microsoft implements its own proprietary client-side storage mechanism, known as “userData,” in IE5 and later. userData enables the storage of medium amounts of string data and can be used as an alternative to Web Storage in versions of IE before IE8.

The File object allows user-selected files to be uploaded through an XMLHttpRequest.

Developers who need to work with really huge amounts of data like to use databases, and the most recent browsers have started to integrate client-side database functionality into their browsers.

The min means the minimised version of the library, with unnecessary comments and whitespace removed, and internal identifiers replaced with shorter ones.

The jQuery() function (a.k.a) $()) is the most important one in the jQuery library. It is heavily overloaded, however, and there are four different ways you can invoke it.

The equivalent replacement of $(document).ready(f) is $(f).

jQuery.noConflict() is the utility function in jQuery.

jQuery.parseJSON() is used for parsing JSON text.

Both img and script contains the src property thatt can be set to initiate an HTTP GET request.

XMLHttpRequest is both an object and a class.

An HTTP request consists of four parts :
1. The HTTP request method or “verb”
2. The URL being requested
3. An optional set of request headers, which may include authentication information
4. An optional request body

The HTTP response sent by a server has three parts :
1. A numeric and textual status code that indicates the success or failure of the request
2. A set of response headers
3. The response body

These features are at the heart of jQuery’s power and utility:
1. An expressive syntax (CSS selectors) for referring to elements in the document
2. An efficient query method for finding the set of document elements that match a CSS selector
3. A useful set of methods for manipulating selected elements
4. Powerful functional programming techniques for operating on sets of elements as a group, rather than one at a time
5. A succinct idiom (method chaining) for expressing sequences of operations.

The code that begins a HTTP GET request for the contents of the specified URL is
request.open("GET","data.csv");

The jQuery library defines a single global function named jQuery(). This function is so frequently used that the library also defines the global symbol $ as a shortcut for it.

It is possible for JavaScript code to script HTTP, however. HTTP requests are initiated when a script sets the location property of a window object or calls the submit() method of a form object. In both cases, the browser loads a new page.

It is possible for JavaScript code to script HTTP, however. HTTP requests are initiated when a script sets the location property of a window object or calls the submit() method of a form object. In both cases, the browser loads a new page.

jQuery() is a factory function rather than a constructor: it returns a newly created object but is not used with the new keyword) jQuery objects define many methods for operating on the sets of elements they represent, and most of this chapter is devoted to explaining those methods.

The code to ask for the set of all div elements in a document is
var divs = $("div");

The css() method operates on the jQuery object returned by $(), and returns that same object, so that the show() method can be invoked next in a compact “method chain.”

The key feature of an Ajax application is that it uses scripted HTTP to initiate data exchange with a web server without causing pages to reload.

Comet is the reverse of Ajax: in Comet, it is the web server that initiates the communication, asynchronously sending messages to the client.

Other names for Comet include “Server Push”, “Ajax Push”, “HTTP Streaming”.