1 function multistep(steps, args, callback){ 2         var tasks = steps.concat(); 3  4         setTimeout(function(){ 5             var task = tasks.shift(); 6  7             task.apply(null, args || []);    // call / aplly 第一个参数是 null或者undefined的时候指向window 或者 Global 8  9             if(tasks.length > 0){            // 检测还有没有其他步骤要处理10                 setTimeout(arguments.callee, 25);11             }else{12                 callback();13             }14         }, 25);15     }16 17     function saveDocument(id,nd){                    // 注意传参18         var tasks = [openDocument, writeText, closeDocument, updateUI];19 20         multistep(tasks, [id, nd], function(){21             console.log("Save completed!");22         });23     }24 25     saveDocument({color : "red"},{name : "NICK"});    // 注意传参26     function openDocument(n,m){console.log(n,m)}27     function writeText(n){console.log(n)}28     function closeDocument(n){console.log(n)}29     function updateUI(n){console.log(n)}