javascript异步解决方案

var cache = {}; function getArticleWithCache ( id, callback ) {     if ( !cache[id] ) {         callback(cache[id]);     } else {         getArticle(id, function( a ){             cache[id] = a;             callback(a);         });     } } 

function backgroundLoad ( ids, callback ) {     var i = 0;     function l ( ) {         if ( i < ids.length ) {             getArticleWithCache(ids[i++], function( a ){                 backgroundLoad(a.children, l);             });         } else {             callback();         }     }     l(); }