deferred.js

(function( jQuery ) {

var // Promise methods
	promiseMethods = "then done fail isResolved isRejected promise".split( " " ),
	// Static reference to slice
	sliceDeferred = [].slice;

jQuery.extend({
	// Create a simple deferred (one callbacks list)
	_Deferred: function() {
		var // callbacks list
			callbacks = [],
			// stored [ context , args ]
			fired,
			// to avoid firing when already doing so
			firing,
			// flag to know if the deferred has been cancelled
			cancelled,
			// the deferred itself
			deferred  = {

				// done( f1, f2, ...)
				done: function() {
					if ( !cancelled ) {
						var args = arguments,
							i,
							length,
							elem,
							type,
							_fired;
						if ( fired ) {
							_fired = fired;
							fired = 0;
						}
						for ( i = 0, length = args.length; i < length; i++ ) {
							elem = args[ i ];
							type = jQuery.type( elem );
							if ( type === "array" ) {
								deferred.done.apply( deferred, elem );
							} else if ( type === "function" ) {
								callbacks.push( elem );
							}
						}
						if ( _fired ) {
							deferred.resolveWith( _fired[ 0 ], _fired[ 1 ] );
						}
					}
					return this;
				},

				// resolve with given context and args
				resolveWith: function( context, args ) {
					if ( !cancelled && !fired && !firing ) {
						// make sure args are available (#8421)
						args = args || [];
						firing = 1;
						try {
							while( callbacks[ 0 ] ) {
								callbacks.shift().apply( context, args );
							}
						}
						finally {
							fired = [ context, args ];
							firing = 0;
						}
					}
					return this;
				},

				// resolve with this as context and given arguments
				resolve: function() {
					deferred.resolveWith( this, arguments );
					return this;
				},

				// Has this deferred been resolved?
				isResolved: function() {
					return !!( firing || fired );
				},

				// Cancel
				cancel: function() {
					cancelled = 1;
					callbacks = [];
					return this;
				}
			};

		return deferred;
	},

	// Full fledged deferred (two callbacks list)
	Deferred: function( func ) {
		var deferred = jQuery._Deferred(),
			failDeferred = jQuery._Deferred(),
			promise;
		// Add errorDeferred methods, then and promise
		jQuery.extend( deferred, {
			then: function( doneCallbacks, failCallbacks ) {
				deferred.done( doneCallbacks ).fail( failCallbacks );
				return this;
			},
			fail: failDeferred.done,
			rejectWith: failDeferred.resolveWith,
			reject: failDeferred.resolve,
			isRejected: failDeferred.isResolved,
			// Get a promise for this deferred
			// If obj is provided, the promise aspect is added to the object
			promise: function( obj ) {
				if ( obj == null ) {
					if ( promise ) {
						return promise;
					}
					promise = obj = {};
				}
				var i = promiseMethods.length;
				while( i-- ) {
					obj[ promiseMethods[i] ] = deferred[ promiseMethods[i] ];
				}
				return obj;
			}
		} );
		// Make sure only one callback list will be used
		deferred.done( failDeferred.cancel ).fail( deferred.cancel );
		// Unexpose cancel
		delete deferred.cancel;
		// Call given func if any
		if ( func ) {
			func.call( deferred, deferred );
		}
		return deferred;
	},

	// Deferred helper
	when: function( firstParam ) {
		var args = arguments,
			i = 0,
			length = args.length,
			count = length,
			deferred = length <= 1 && firstParam && jQuery.isFunction( firstParam.promise ) ?
				firstParam :
				jQuery.Deferred();
		function resolveFunc( i ) {
			return function( value ) {
				args[ i ] = arguments.length > 1 ? sliceDeferred.call( arguments, 0 ) : value;
				if ( !( --count ) ) {
					deferred.resolveWith( deferred, args );
				}
			};
		}
		if ( length > 1 ) {
			for( ; i < length; i++ ) {
				if ( args[ i ] && jQuery.isFunction( args[ i ].promise ) ) {
					args[ i ].promise().then( resolveFunc(i), deferred.reject );
				} else {
					--count;
				}
			}
			if ( !count ) {
				deferred.resolveWith( deferred, args );
			}
		} else if ( deferred !== firstParam ) {
			deferred.resolveWith( deferred, length ? [ firstParam ] : [] );
		}
		return deferred.promise();
	}
});

})( jQuery );