// = > 1、常规方法：

  function sum(arg) {
    var newary = [];

    //类数组转换为数组
    if (arg instanceof Array){
        console.log("传参方式是数组");
        for (var i = 0; i < arg.length; i++) {
            newary.push(arg[i]);
        }
    }else {
        console.log('传参方式是多个数字');
        for (var i = 0; i < arguments.length; i++) {
            newary.push(arguments[i]);
        }
    }

    //数组从小到打排序
    newary.sort(function (a,b) {
        return a-b;
    });
    //删除数组开头的最小项
    newary.shift();
    //删除数组末尾最大项
    newary.pop();
   //循环求和
    var result  = 0;
    for (var i = 0; i < newary.length; i++) {
        result += newary[i];
    }
    //求平均数，并返回结果
    return Math.round(result/newary.length);
}

var result1 = sum(156,423,90,5,24,66,450,25,4,86,76,64,5,88,63,33,42,34,46,19,48,35,70);
console.log(result1);  // => 71.33333333333333

var arr = [1,2,3,4,5,6,7,8,9];
var result2 = sum(arr);
console.log(result2);    // => 5

// = > 常规方法改进：1.0版

   function sum(arg) {
    //类数组转换为数组
    if (arg instanceof  Array) {
        var newary =  Array.prototype.slice.apply(arg);
    }else {
        var newary =  Array.prototype.slice.call(arguments);
    }
    //数组从小到打排序
    newary.sort(function (a,b) {
        return a-b;
    });
    //删除数组开头的最小项
    newary.shift();
    //删除数组末尾最大项
    newary.pop();

    //求平均数，并返回结果
    return (eval(newary.join('+'))/newary.length).toFixed(2)
}

var result1 = sum(156,423,90,5,24,66,450,25,4,86,76,64,5,88,63,33,42,34,46,19,48,35,70);
console.log(result1);    // = >71.33

var arr = [1,2,3,4,5,6,7,8,9];
var result2 = sum(arr);
console.log(result2);      // = >5.00

// = > 常规方法改进：2.0版

   function sum(arg) {
    console.log(arg instanceof Array);
    if (!(arg instanceof Array)) {
        console.log("如果不是数组，执行下面语句");
        var newary = Array.prototype.sort.call(arguments, function (a,b) {return a - b;});
    } else {
        console.log("如果是数组，执行下面语句");
        var newary = Array.prototype.sort.apply(arguments[0],function (a,b) { return a-b;});
    }
    //删除数组开头的最小项
    Array.prototype.shift.call(newary);
    //删除数组末尾最大项
    Array.prototype.pop.call(newary);
    //求平均数，并返回结果
    return (eval([].join.call(newary,'+')) / newary.length).toFixed(2)
}

var result1 = sum(156, 423, 90, 5, 24, 66, 450, 25, 4, 86, 76, 64, 5, 88, 63, 33, 42, 34, 46, 19, 48, 35, 70);
console.log(result1);    // => 71.33

var arr = [1,2,3,4,5,6,7,8,9];
var result2 = sum(arr);
console.log(result2);    //=>5.00