'use strict';

var arr2 = ['小明', '小红', '大军', '阿黄'];
arr2.sort();
console.log('欢迎' + arr2.slice(0, 3) + '和' + arr2.slice(arr2.length - 1) + '同学!');
console.log('欢迎' + arr2.slice(0, 3) + '和' + arr2.slice(-1) + '同学!');
console.log('欢迎' + arr2.slice(0, 3) + '和' + arr2[arr2.length - 1] + '同学!');