Add promise next method

lib/util.js

@@ -4,6 +4,7 @@ var jQuery = require("jquery-deferred")
 
 exports.parseArgs = parseArgs;
 exports.extend = extend;
+exports.next = next;
 
 function parseArgs (args) {
 	var all = slice.call(args, 0)
@@ -82,3 +83,56 @@ function extend(object, fromObject, getters, ignores, originalName, setters) {
 	} );
 }
 
+/**
+ * next
+ *
+ * run promise object step by step.
+ *
+ * next( aPromise )
+ * 	.next( function( aValue ){
+ * 		return bPromise;
+ * 	} )
+ * 	.next( function( aValue, bValue ){
+ * 		return cPromise;
+ * 	} )
+ * 	.done( function( aValue, bValue, cValue ){
+ * 	} )
+ * 	.fail( errorCallback );
+ *
+ * @param {Function} firstParam first can be a Promise object
+ * @return {Promise}  
+ *
+ */
+
+function next ( firstParam ) {
+	if( ! jQuery.isFunction( this.promise ) ) {
+		//The first deferred
+		var promise = jQuery.isFunction( firstParam ) ? firstParam() : firstParam;
+		promise.next = next;
+		return promise;
+	} 
+	var dfd = jQuery.Deferred();
+	this.done( function() {
+		var last = slice.call( arguments )
+			, res;
+		try{
+			res = firstParam.apply( null, last );
+		} catch( e ) {
+			res = e;
+		}
+		jQuery.isFunction( res && res.promise ) ?
+			res.done( function() {
+				var args = slice.call( arguments );
+				for (var i = last.length - 1; i >= 0; i--) {
+					args.unshift( last[i] );
+				}
+				dfd.resolve.apply( dfd, args );
+			} ).fail( dfd.reject )
+			: dfd.reject( res );
+
+	} ).fail( dfd.reject );
+
+	var promise = dfd.promise();
+	promise.next = next;
+	return promise; 
+}