check prime have or not

var num=29;
var rem,i;
var flag=0;
for(i=2;i<=Math.sqrt(num);i++)
{
if(num%i==0)
{
flag++;
}
}
console.log(flag);
if(flag==1)
{
console.log("this is not prime Number "+ num);

}
else
{
console.log("this is prime Number "+ num);
}