// flatern 是摊平数组
    function flat(arr) {
        const isDeep = arr.some(item => item instanceof Array)
        if(!isDeep){
            return arr
        }
        const result = Array.prototype.concat.apply([],arr)
        return flat(result)
    }

    const res = flat([1, 2, [3, 4], 5, [6, 7, [8, 9]]])
    console.log(res)