5.求和和取最值

5-1reduce()归并求和

 var arr=[1,2,3,4];
        var sum=arr.reduce((a,b)=>{
            return a+b;
        })
             console.log(sum);//10
             console.log(arr);//[1,2,3,4]

5-2Math max()取最大值

  var arr=[1,2,3];
console.log(Math.max(12,3,4));//12
console.log(Math.max(...arr));//要先展开数组，才可以找最大值 3

5-3Math.min()取最小值

var arr=[5,4,3,2];
console.log(Math.min(...arr));
//算法
 var arr=[5,4,3,2];
        var minNum=arr[0]
        for(var i=1;i<arr.length;i++){
            if(minNum>arr[i]){
                minNum=arr[i]
            }
        }
        console.log(minNum);