title: Let for ES6 in for loop has some issues?
body: <p><img src="https://i.stack.imgur.com/GaQWA.png" alt="enter image description here"></p>
  
  <p><img src="https://i.stack.imgur.com/p8jpI.png" alt="enter image description here"></p>
  
  <p>According to the first image, we can find that i has been declared ,why we can use 'let' to declare it again?</p>