SOURCE

//1.
var str ="Rome was not built in a day";
      var arr =str.replaceAll(" ","");//去掉所有的空格
      var sum =0;
      for(var i of arr)
      {
        sum++;
      }
      document.write(sum+"</br>");
//2.
function AbccbA(stringAbc) {
     var stringcbA='';
     for(var i=stringAbc.length-1;i>=0;i--){
         stringcbA=stringcbA.concat(stringAbc.charAt(i));
    }
    return stringcbA;
}

document.write(AbccbA("sdadsd")+"</br>");

//3.
//for循环
function Cumsum(){
    var sum=0;
    //for循环
    for(var i=0;i<=100;i++){
        sum+=i;
    }
    return sum;
}
document.write(Cumsum()+"</br>");
//while循环
function Cumsum1(){
    var sum=0;
    //for循环
    var i=0;
    while(i<100){
        i++;
        sum+=i;
    }
    return sum;
}
document.write(Cumsum1()+"</br>");
//do while 循环
function Cumsum2(){
    var sum=0;
    //for循环
    var i=0;
    do{
        i++;
        sum+=i;
    }while(i<100);
    return sum;
}
document.write(Cumsum2()+"</br>");