文章目录

• 数组对象
• • • 1. 数组对象之遍历
    • 2. 数组对象之过滤
    • 3. 数组对象之.map()

数组对象

首先定义一个数组对象

let student = [
  {id:1,name:'小明',number:1001,test:60},
  {id:2,name:'小红',number:1002,test:70},
  {id:3,name:'小黄',number:1003,test:55},
  {id:4,name:'小蓝',number:1004,test:90},
  {id:5,name:'小紫',number:1005,test:59},
  {id:6,name:'小粉',number:1006,test:61}
]

1. 数组对象之遍历

for…of

//遍历数组对象
for (let item of student) {
  console.log('name', item.name)
  console.log('test', item.test) 
}

可用于判断某个学号为xxxx的学生的成绩？

//提取学号为1002的学生的成绩
let test
for (let item of student) {
  if (item.number == 1002) {
    test = item.test
  }
}
console.log('1002学生的成绩为',test)

2. 数组对象之过滤

filter函数

//过滤及格的人
let passStudent = student.filter(el => el.test >= 60)
console.log('passStudent', passStudent)

filter用法二

let student = [
  {id:1,name:'小明',number:1001,test:60},
  {id:2,name:'小红',number:1002,test:70},
  {id:3,name:'小黄',number:1003,test:55},
  {id:4,name:'小蓝',number:1004,test:90},
  {id:5,name:'小紫',number:1005,test:59},
  {id:6,name:'小粉',number:1006,test:61}
]

let patient = [
  {id:2021001,name:'小明',illnessId:'10000000000'},
  {id:2021002,name:'小黄',illnessId:'10000000001'},
  {id:2021003,name:'小绿',illnessId:'10000000002'},
  {id:2021004,name:'小新',illnessId:'10000000003'},
  {id:2021005,name:'小思',illnessId:'10000000004'}
]
//查找两个数组对象的交集
let intersection = student.filter(bp => {
  if (patient.findIndex(lp => lp.name == bp.name) != -1)  
    return {
      ...bp
    }
})
console.log('intersection', intersection)

其中findIndex()函数用法

回调函数有三个参数。value：当前的数组元素。index：当前索引值。arr：被查找的数组。

当条件为true时findIndex()返回索引值，如果没有符合条件元素时findIndex()返回的是-1

3. 数组对象之.map()

.map() 通过指定函数调用一个数组中每一项元素，来创建一个新数组

1.返回对象中的部分数据：例如返回id和name列

let passstudentin = []
passstudentin = student.map(bp => {
  return {
    id: bp.id,
    name: bp.name
  }
})
console.log('passstudentidname', passstudentin)

2. 对象数组去重

let student = [
  {id:1,name:'小明',number:1001,test:60},
  {id:2,name:'小红',number:1002,test:70},
  {id:3,name:'小黄',number:1003,test:55},
  {id:4,name:'小蓝',number:1004,test:90},
  {id:5,name:'小紫',number:1005,test:59},
  {id:6,name:'小粉',number:1006,test:61},
  {id:6,name:'小粉',number:1006,test:61},
]
//去重
let map = new Map()
student.forEach((item,index)=>{
  if (!map.has(item['id'])){
    map.set(item['id'],item)
  }
})
console.log([...map.values()])

3. 给符合条件的对象添加元素

//当某学生生病时，在student对象中添加illness:true
let whoillness = student.map(bp => {
  if (patient.findIndex(lp => lp.name == bp.name) != -1)
    return {
      ...bp,
      illness: true
    }
  return bp
})
console.log('whoillness', whoillness)