how to loop on var javascript code example

Example 1: javascript for loop

for (var i; i < 10; i++) {
  
}

Example 2: for in range javascript

function* range(start=0, end=null, step=1) {
  if (end == null) {
    end = start;
    start = 0;
  }

  for (let i=start; i < end; i+=step) {
    yield i;
  }
}