Use for loop to find prime numbers within 1000

var n=0;
for(var i=2;i<=1000;i++){
  var zhishu=true;

for(var j=2;j<i;j++){
    if(i%j==0){
     zhishu=false;
     break;
     }
    }
    if(zhishu==true){
     document.write(i+"<br>");
   n++
}
  }
   alert(n)