js-数组内置函数-filter、map、forEach、reduce

1、过滤数组 -filter

筛选数组元素，并生成新数组

//过滤出分数为60分以上的数据
<script>
    const arr = [
      {'name':'张三','score':80},
      {'name':'张六','score':50},
      {'name':'李四','score':90},
      {'name':'王五','score':60},
    ]

    const newArr = arr.filter(function(item,index){
      return item.score>=60
    }) 

    console.log(newArr)
</script>

2、迭代数组-map

返回新数组，新数组里面的元素是处理之后的值，经常用于处理数据

<script>
  //给数据的分数都加上10分
  const arr = [
    {'name':'张三','score':80},
    {'name':'张六','score':50},
    {'name':'李四','score':90},
    {'name':'王五','score':60},
  ]

  arr.map(function(item,index){
    item.score+=10
  }) 

  console.log(arr)
</script>

3、遍历数组-forEach

不返回，用于不改变值，经常用于查找打印输出值

<script>
  //遍历数组
  const arr = [
    {'name':'张三','score':80},
    {'name':'张六','score':50},
    {'name':'李四','score':90},
    {'name':'王五','score':60},
  ]

  arr.forEach(function(item,index){
    console.log(item.name)
  }) 
</script>

4、累计器-reduce

返回函数累计处理的结果，经常用于求和等

//语法：arr.reduce(function(累计值, 当前元素){}, 起始值)

// prev=5初始化值
<script>
  const arr = [1, 2, 3]
  const re = arr.reduce((prev, item) => prev + item,5)
  console.log(re)
</script>