lets.js

for (let i = 0; i < 3; i++) {
   console.log(i);
  for (let i = 10; i < 13 i++) {
    console.log(i);
    for (let i = 100; i < 103; i++) {
      console.log(i);
    }
  }
}
// 
/* 
   (1st)0, 
     (2nd)10, 
       (3rd)100, (3rd)101, (3rd)102, 
     (2nd)11, 
       (3rd)100, (3rd)101, (3rd)102, 
     (2nd)12, 
       (3rd)100, (3rd)101, (3rd)102, 
   (1st)1, 
     (2nd)11, 
        ...... 
*/