简单明了的闭包

function Foo() {
  const a = 1
  return function father() {
    const b = 2
    return function() {
      const c = 3
      console.log(a, b, c)
    }
  }
}
const fn = Foo()()
fn()

打三个断点 变量a,b所在的作用域Closure被保存起来拉