数组的相关处理

idList = [...new Set(idList)]

2. 对象数组根据某个元素去重

idList = [...new Set(idList.map(item => item.xxx))]

3. 对比数组,取出不同元素成新数组

let arr1 = [4,6,7], arr2 = [5,6,7]
let newArr = arrA .concat(arrB ).filter((cur, i, arr) => {
    return arr.indexOf(cur) === arr.lastIndexOf(cur);
})  // c = [4,5]

4. 对比数组, 计算数组中拥有某个相同属性的元素个数 (如age)

	let originList = [
		{age:15,name:'张三'},
		{age:15,name:'李四'},
		{age:14,name:'赵五'}
	]
    let newArr = [...new Set(originList .map(item => item.age))] // 按需去重
    console.log(newArr, 'newArr') // [15,14]
    let cateList = [] // 归类分组
    let countList = [] // 计算个数 
    newArr.map(i => {
      cateList .push(originList .filter(t => t.age=== i))
    })
    cateList .map((i, index) => {
      countList.push({
        age: newArr[index],
        num: i.length,
      })
    })
    console.log(cateList , 'cateList ') //  [ [{age: 15, name: "张三"},{age: 15, name: "李四"}],[{age: 14, name: "赵五"}] ]
    console.log(countList, 'countList') // [{age: 15, num: 2},{age: 14, num: 1}]