SOURCE

function writeDocument(variable) {
    document.write(variable + "<br/>");
}


//第一种循环 for
var n = 1;
var sum = 0;
for (; n <= 100; n++) {
    sum += n;
}
writeDocument("for循环: " + sum);


//第二种循环 while
var n1 = 1;
var sum1 = 0;
while (n1 <= 100) {
    sum1 += n1;
    n1++;
}
writeDocument("while循环: " + sum1);


//第三种循环 do while
var n2 = 1;
var sum2 = 0;
do {
    sum2 += n2;
    n2++;
} while (n2 <= 100);
writeDocument("do while循环: " +sum2);