redefine variable when converting let to var

[guoerwei]

{
  let count = 0;
  setInterval(() => {
    console.log('first tick: ', ++count);
  }, 200);
}
{
  let count = 0;
  setInterval(() => {
    console.log('second tick: ', ++count);
  }, 300);
}

with babili, will simply converts to

{
  var a = 0;
  setInterval(function() {
    console.log('first tick: ', ++a)
  }, 200)
}
{
  var a = 0;
  setInterval(function() {
    console.log('second tick: ', ++a)
  }, 300)
}

and getting variable redefined

[hzoo]

Hey @guoerwei! We really appreciate you taking the time to report an issue. The collaborators
on this project attempt to help as many people as possible, but we're a limited number of volunteers,
so it's possible this won't be addressed swiftly.

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