SOURCE

//第一种for循环
var n = 1;
var sum = 0;
for (; n <= 100; n++){
    sum += n;
    }
document.write("for循环:"+'<br/>');    
document.write(sum+'<br/>');

//第二种while循环
var n = 1;
var sum = 0;
while(n<=100){
    sum += n;
    n++;
    }
document.write("while循环:"+'<br/>');    
document.write(sum+'<br/>');

//第三种 do while
var n = 1;
var sum = 0;
do{
    sum += n;
    n++;
    } 
    while (n <= 100);
document.write("do while循环:"+'<br/>'); 
document.write(sum);