多维数组展平成一维数组

      let arr = [1, [2, [3, [4, 5]]], [6, 7, [8, 9, [11, 12]], 10]]
      let result = [],
        fn = function (arr) {
          if (arr.length === 0) return
          for (let i = 0; i < arr.length; i++) {
            let item = arr[i]
            if (typeof item === 'object') {
              fn(item)
            } else {
              result.push(item)
            }
          }
        }
      fn(arr)
      console.log(result)

reduce

   const fatter = (arr) => {
        return arr.reduce((pre, cur) =>
          pre.concat(Array.isArray(cur) ? fatter(cur) : cur), []
        )
      }