let a = 0

function main() {
  let b = 0;

  const func = () => {
    console.log(a, b);

    let c = 0;

    const subFunc = () => console.log(b, c)

    c = b = 10;

    subFunc()
  }

  b = 5;            

  func()            
}

a = 5

main()

// 5 5  10 10