JavaScript递归及浅拷贝深拷贝

1 递归执行模型
function fn1 () {
  console.log(111)
  fn2()
  console.log('fn1')
}
function fn2 () {
  console.log(222)
  fn3()
  console.log('fn2')
}
function fn3 () {
  console.log(333)
  fn4()
  console.log('fn3')
}
function fn4 () {
  console.log(444)
  console.log('fn4')
}
fn1()
2 例子：计算阶乘的递归函数
function factorial (num) {
  if (num <= 1) {
    return 1
  } else {
    return num * factorial(num - 1)
  }
}
3 递归应用场景案例

浅拷贝
深拷贝
菜单树
遍历 DOM 树