<script>
        function sum(num){
            return function(num2){
                return num+num2
            }
        }

        console.log(sum(1)(2))
    </script>

面试考察

只要参数够了 达到某个数量就输出

<script>
        let nums=[]
        function sum(...args){
            nums.push(...args)
            if(nums.length>=5){
                const out = (nums.slice(0,5).reduce((prev,res)=>{return res+=prev},0))
                //  累加之后清空数组
                nums = []
                return out
            }
            else{
                return sum
            }
        }
        console.log(sum(1,1,1)(1,1))
    </script>

调优

<script>
        function sumMaker(len){
            let nums = []
            function mySum(...args){
                nums.push(...args)
                if(nums.length>=len){
                    const res = nums.slice(0,len).reduce((prev,out)=>{return out+=prev},0)
                    nums=[]
                    return res
                }
                else{
                    return mySum
                }

            }

            return  mySum

        }

        console.log(sumMaker(4)(1,2)(3,4))

    </script>

实际应用

    <script>
        const typeOfTest = function(TYPE){
            
            function isUndefined(thing){
                return typeof thing === TYPE
            }
            return isUndefined
        }

    </script>