SOURCE

/* while循环 */
var sum=0
var i=1
while(i<=100){
    sum+=i;
    i++;
}
document.write("sum="+sum)
document.write(" <br/>");
/* do-while循环 */
var i=1
var sum=0
do{
    sum=sum+i
    i++
}while(i<=100)
document.write("sum="+sum)
document.write(" <br/>");
/*for循环 */
var sum=0
for(var i=1;i<=100;i++){
    sum+=i;
}
document.write("sum="+sum+"<br/>")