node sync question

var fs=require('fs');
var path="log.txt";
try {
  fs.unlinkSync(path);
}catch(err) {}

//從0寫到1000
for(var i=0;i<1000;i++){
    fs.appendFile(path,i+",",function(err){
        if(err) console.log(err);
    });
}

//檢查檔案是否為0到1000
setTimeout(function(){
    fs.readFile(path,"utf8",function(err,data){
        if(err){
            console.log(err);
            return;
        }
        var arr=data.split(",");
        var lnum=-1;
        for(var k in arr){
            if(arr[k]!=""){
                var next=parseInt(arr[k]);
                if(lnum+1!=next){
                    err++;
                    console.log("err: "+lnum+","+next);
                }
                lnum=next;
            }
        }
        console.log("All ERR: "+err);
    });
},1000);