var arr = [{
      key: '01',
      value: '乐乐'
   }, {
      key: '02',
      value: '博博'
   }, {
      key: '03',
      value: '淘淘'
   },{
      key: '04',
      value: '哈哈'
   },{
      key: '01',
      value: '乐乐'
   }];


   //  方法1：利用对象访问属性的方法，判断对象中是否存在key
   var result = [];
   var obj = {};
   for(var i =0; i<arr.length; i++){
      if(!obj[arr[i].key]){
         result.push(arr[i]);
         obj[arr[i].key] = true;
      }
   }
   console.log(result); // [{key: "01", value: "乐乐"},{key: "02", value: "博博"},{key: "03", value: "淘淘"},{key: "04", value: "哈哈"}]

/**
		 * 按照List中的某个String类型的属性进行排序
		 * 
		 * @param list
		 */

		Collections.sort(classList, new Comparator() {
			@Override
			public int compare(Object o1, Object o2) {
				ExamineeClass e1 = (ExamineeClass) o1;
				ExamineeClass e2 = (ExamineeClass) o2;
				return e1.getClassName().compareTo(e2.getClassName());
			}
		});
		
		
		按照List中的某个String类型的属性进行去重
List<User> userListNoDupAndSort = removeDuplicateUser(userList);
		 private static ArrayList<User> removeDuplicateUser(List<User> users) {
        Set<User> set = new TreeSet<User>(new Comparator<User>() {
            @Override
            public int compare(User o1, User o2) {
                //字符串,则按照asicc码升序排列
                return o1.getUserId().compareTo(o2.getUserId());
            }
        });
        set.addAll(users);
        return new ArrayList<User>(set);
    }
	
	
Java  8 去重
	users.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(()->newTreeSet<>(Comparator.comparing(User::getUserId))), ArrayList::new))
 

 

在后台管理中，遇到有些情况，需要根据数组中对象的某个属性去重，如id、name… 方法如下：
let hash = {};
// this.selectList是需要去重的数组
// curVal.id代表根据对象的id去重
this.selectList = this.selectList.reduce((preVal, curVal) => {
    hash[curVal.id] ? '' : hash[curVal.id] = true && preVal.push(curVal);
    return preVal
}, [])

function uniqueFunc(...args) {
	const paramsLength = arguments.length;
	if(paramsLength == 1) {
		return [...new Set(arr)];
	} else {
		const res = new Map();
		const flag = arguments[1];
		return arguments[0].filter(item => !res.has(item[flag]) && res.set(item[flag], item));
	}
}

let arr = [1,2,3,4,5,2];

uniqueFunc(arr);

/** 输出
 * [1,2,3,4,5]
 */

let stus = [
    {id: 12, name: 'z'},
    {id: 2, name: 'ss'},
    {id: 3, name: 'z'},
    {id: 12, name: 'cc'}
]

uniqueFunc(stus, 'id');
/** 输出
 * [
    {id: 12, name: 'z'},
    {id: 2, name: 'ss'},
    {id: 3, name: 'z'}
    ]
 */