归类函数以及封装

基础题

({} + {}).length => '[object Object][object Object]' 30
([] + []).length => '' 0
(function(){}).length => 0 函数length属性( 形参个数 )

对后台一些数据进行归类

let colors = [
      {id:'1', name:'red'},
      {id:'2', name:'blue'},
          {id:'3', name:'green'},
          {id:'4', name:'pink'}
    ],
    persons = [
      {name: '小红', clothColor:'1,3'},
      {name: '小田', clothColor:'1,2'},
      {name: '小付', clothColor:'2,4'},
      {name: '小冯', clothColor:'3,4'}
    ];
//根据哪个种类，就先遍历哪个数组
function classingFn(){
    let cache = {};
  colors.forEach((elem)=>{
      let _id = elem.id;
        cache[_id] = [];
    //遍历数据，进行分类
    persons.forEach((person)=>{
      let clothColorsArr = person.clothColor.split(',');
        if( clothColorsArr.includes(_id) ){
          cache[_id].push(person)
      }
    })
  })
  return cache
}
console.log(classingFn())

归类函数的封装，可以使用偏函数，先将关联数据传入，返回一个等待后续参数执行的函数。
考虑点：
（1）单一归类还是复合归类
（2）关联数据以什么字段进行归类

let colors = [
      {id:'1', color:'red'},
      {id:'2', color:'blue'},
          {id:'3', color:'green'},
          {id:'4', color:'pink'}
    ],
    persons = [
      {name: '小红', clothColor:'1,3'},
      {name: '小田', clothColor:'1,2'},
      {name: '小付', clothColor:'2,4'},
      {name: '小冯', clothColor:'3,4'}
    ];
function classification ( sortArr, Data ){
    return function(foreign_key, sortingType){
    let cache = {};
      //先校验排序类别参数
    let correctSortingTypes = [ 'single', 'multi' ],
        isTypeCorrect = correctSortingTypes.includes(sortingType);
    if(!isTypeCorrect){
        let errorObj = new Error('invalid sortingType, only "single"  and "multi" are accepted');
      console.log(errorObj);
      return
    }
    //先遍历分类数据
    sortArr.forEach((item)=>{
        let _id = item.id;
      cache[_id] = [];
      //遍历数据，进行分类
      Data.forEach((elem)=>{
        //判断归类类别
        let foreign_val = elem[foreign_key];
        if(sortingType === 'single'){
                        if(  _id === foreign_val){ cache[_id].push(elem) }
        }else{
            let arr = foreign_val.split(',');
          arr.forEach((singleId)=>{
              if(_id === singleId){ cache[_id].push(elem) }
          })
        }
      })
    })
        return cache
  }
}