SOURCE

//1 .for循环
        var result = 0;
        for (var i = 0; i <= 100; i++) {
            result += i;
        }

    document.write(result);
    document.write("<br />");

    //2. while()循环
        var result2 = 0;
        var i = 0;
        while (i <= 99) {
            i++;
            result2 += i;
        }

    document.write(result2);
    document.write("<br />");


    //    do-while语句
        var result3 = 0;
        var i = 0;
        do {
            i++;
            result3 += i;
        }
        while (i <= 99);

    document.write(result3)