ES6（十）map、set与数组和对象的比较

Map和数组的对比

let map = new Map()
let array = []
// 增
map.set('t', 1)
array.push({t: 1})
console.log('add', map, array)
// 查
let mapExist = map.has('t')
let arrayExist = array.find(item => item.t)
console.log('get', mapExist, arrayExist)
// 改
map.set('t', 2)
array.forEach(item => {
  item = item.t ? item.t = 2 : ''
  return item
})
console.log('modify', map, array)
// 删
map.delete('t')
array.splice(array.findIndex(item => item.t), 1)
console.log('remove', map, array)

set和数组的对比

let set = new Set()
let array = []
// 增
set.add({t: 1})
array.push({t: 1})
console.info('add', set, array)
// 查
let setExist = set.has({t: 1})
let arrayExist = array.find(item => item.t)
console.info('get', setExist, arrayExist)
// 改
set.forEach(item => {
  item = item.t ? item.t = 2 : ''
  return item
})
array.forEach(item => {
  item = item.t ? item.t = 2 : ''
  return item
})
console.info('modify', set, array)
// 删
set.forEach(item => {
  item = item.t ? set.delete(item) : ''
  return item
})
array.splice(array.findIndex(item => item.t), 1)
console.info('delete', set, array)


map、set和对象的使用比较

let item = {t: 1}
let map = new Map()
let set = new Set()
let obj = {}

// 增
map.set('t', 1)
set.add(item)
obj.t = 1
console.log('add', map, set, obj)
// 查
console.info({
  action: 'get',
  mapExist: map.has('t'),
  setExist: set.has(item),
  objExist: 't' in obj
})
// 改
map.set('t', 2)
item.t = 2
obj.t = 2
console.log('modify', map, set, obj)
// 删
map.delete('t')
set.delete(item)
delete obj.t
console.log('remove', map, set, obj)

示例

      let json1 = {"name":"ES6","day":"2014","feature":"新特性"};
      //json 2 map
      let map1 = new Map();
      for(let i in json1){
        map1.set(i,json1[i]);
      }
      console.log(map1);

      //map 2 json
      let map = new Map();
      map.set("name","ES6");
      map.set("day","2014");
      map.set("feature","新特性");
      let json = {};
      for(let [k,v] of map){
        json[k]=v;
      }
      console.log(json);

      const num = 1000000;
      let a = {};
      for(let i = 0;i<num;i++){
        a[`element${i}`]=i;
      }
      let start_time = new Date();
      for(let key in a){
        a[key]+=1;
      }
      let end_time = new Date();
      console.log("time cost:",end_time-start_time);

      const num = 1000000;
      let a = new Map();
      for(let i = 0;i<num;i++){
        a.set(`element${i}`,i);
      }
      let start_time = new Date();
      for(let key of a.keys()){
        a.set(key,a.get(key)+1);
      }
      let end_time = new Date();
      console.log("time cost:",end_time-start_time);

循环方式

projectMap.forEach(function (value, key, map) {
    //value和key就是map的key，value，map是map本身
});

去重

let arr = [4, 1, 3, 3, 2, '2'];
let uniqueArr = [...new Set(arr)];
console.log(uniqueArr); // [4, 1, 3, 2, "2"]

that.dataInfo = [...new Set(that.dataInfo.concat([], res.data.data.result))]
let newArr = Array.from(that.dataInfo)
console.log(newArr)

 

 转换

// map转object
let obj= Object.create(null);
for (let[k,v] of map) {
    obj[k] = v;
}

// object转json
JSON.stringify(obj);