js 性能优化之快速响应的用户界面

function processArray(items,process,callback){
 var todo = items.concat();
 setTimeout(function(){
 process(todo.shift());
 
 if(todo.length > 0){
 setTimeout(arguments.callee,25);
 } else {
 callback(items);
 }
 },25);
}
var items = [1,2,3];
function output(value){
 console.log(value);
} 
processArray(items,outputValue,function(){
 console.log('finished output!')
});

function multistep(steps,args,callback){
 var tasks = steps.concat();
 setTimeout(function(){
 var task = tasks.shift();
 task.apply(null,args||[]);
 
 if(tasks.length > 0){
 setTimeout(arguments.callee,25);
 } else {
 callback();
 }
 },25);
}
function saveDocument(id){
 var tasks = [open,write,close];
 multistep(tasks,[id],function(){
 console.log('finished!');
 })
} 

function timeProcessArray(items,process,callback){
 var todo = items.concat();
 setTimeout(function(){
 var start = +new Date();
 do{
 process(todo.shift());
 }while(todo.length > 0 &&(+new Date() - start < 50)) ;
 if(todo.length > 0){
 setTimeout(arguments.callee,25);
 } else {
 callback(items);
 }
 },25);
}