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);
}