es6数组去重、数组中的对象去重 && 删除数组（按条件或指定具体元素 如：id）&& 筛选去掉没有子组件的父组件

// 数组去重
{
   const arr = [1,2,3,4,1,23,5,2,3,5,6,7,8,undefined,null,null,undefined,true,false,true,‘中文‘,‘‘,‘‘,‘hello‘,‘中文‘];
   //  第一种
   const r = [...new Set(arr)];
   console.log(r); // [1, 2, 3, 4, 23, 5, 6, 7, 8, undefined, null, true, false, "中文", "", "hello"]

   // 第二种
   const R = arr.reduce((all,name) => all.includes(name) ? all :[...all,name],[]);
   console.log(R); // [1, 2, 3, 4, 23, 5, 6, 7, 8, undefined, null, true, false, "中文", "", "hello"]

   // 第三种
   const k = arr.filter((item, i) => i === arr.indexOf(item));
   console.log(k); // [1, 2, 3, 4, 23, 5, 6, 7, 8, undefined, null, true, false, "中文", "", "hello"]
}

// 统计每个元素在数组中出现的次数
{
   const arr = [‘zhangsan‘, ‘lisi‘, ‘wangwu‘, ‘zhangsan‘, ‘lisi‘, ‘wangwu‘,‘zhaosi‘,‘liuneng‘];
   const r = arr.reduce((all, name) =>{
      if(name in all){
         all[name]++
      }else{
         all[name] = 1;
      }
      return all;
   },{})；
   console.log(r); // {zhangsan: 2, lisi: 2, wangwu: 2, zhaosi: 1, liuneng: 1}
}

// 数组对象去重
{
   const arr = [
      {
         name:‘zhangsan‘,
            age:12
      },
        {
         name:‘lisi‘,
         age:14
      },
      {
         name:‘zhangsan‘,
            age:12
      },
        {
         name:‘lisi‘,
         age:14
      },
      {
         name:‘zhangsan‘,
            age:12
      },
        {
         name:‘lisi‘,
         age:14
      },
      {
         name:‘zhangsan‘,
            age:12
      },
        {
         name:‘wangwu‘,
         age:16
      },
      {
         name:‘wagnwu‘,
            age:16
      },
        {
         name:‘lisi‘,
         age:14
      },

   ]

   // 根据 age 去重
    // 方法一
    const age = ‘age‘;
   const r = arr.reduce((all, next) => all.some((atom) => atom[age] == next[age]) ? all : [...all, next],[]);
   console.log(r);

}

//指定具体元素//删除id=5的
let arr = [
        { id: 1, name: '北京' },
        { id: 2, name: '上海' },
        { id: 3, name: '深圳' },
        { id: 4, name: '广州' },
        { id: 5, name: '青岛' }
      ]
arr.splice(arr.findIndex(item=>item.id==5),1)

//find方法用于查找第一个符合条件的数组成员,如果没有找到返回undefind

    let target = arr.find((item,index) => {
        return item.id ==1
    })
    console.log(target)

//删除id大于3的(只保留小于等于3)
let arr2 = arr.reduce((total, current) => {
    current.id<= 3 && total.push(current);
    return total;
}, []);

　　

//筛选去掉没有子组件的父组件 （parentId为0代表是父组件）
let arr = [
    {
        name:'1',
        id:1,
        parentId:0
    },{
        name:'3',
        id:3,
        parentId:0
    },{
        name:'2',
        id:2,
        parentId:0
    },{
        name:'1333',
        id:13,
        parentId:1
    },{
        name:'2444',
        id:24,
        parentId:2
    }]
    arr = arr.filter((x, index, self)=>{
        // x : 数组每一项的值
        // index: 每一项的下标
        // self: 当前数组
      return x.parentId!=0 || self.some((atom) =>  atom['parentId'] == x['id'] )
    })