Question

我从一个数组开始，想要查看该数组中是否已存在该键。

keys = ['pitch1']

var y = [
  {header: 'pitch1', data: 'pitch1 data'}, 
  {header: 'pitch3', data: 'pitch3 data'}, 
  {header: 'pitch4', data: 'pitch4 data'},
  {header: 'pitch2', data: 'pitch2 data'},
  {header: 'pitch1', data: 'more pitch 1 data'},
]


y.map((item, index) => {
  if (keys.indexOf[item.header]) {
    console.log('found it')
  } else {
    console.log('not found')
  }
})

这是回归：

"not found"
"not found"
"not found"
"not found"
"not found"

我做错了什么？

Answer 1

您的indexOf函数正在返回0。

0是Javascript中的假值。改变你的状况如下：

if (keys.indexOf(item.header) >= 0)

Answer 2

keys.indexOf[item.header]应为keys.indexOf(item.header)并将{if条件}更改为if (keys.indexOf(item.header) != -1) indexOf，当它找不到对象时返回-1

它返回-1而不是false的原因是字符串开头的针位于0位置，相当于Javascript中的false 。因此，返回-1可确保您知道实际上没有匹配。

keys = ['pitch1']

var y = [
  {header: 'pitch1', data: 'pitch1 data'}, 
  {header: 'pitch3', data: 'pitch3 data'}, 
  {header: 'pitch4', data: 'pitch4 data'},
  {header: 'pitch2', data: 'pitch2 data'},
  {header: 'pitch1', data: 'more pitch 1 data'},
]


y.map((item, index) => {
  if (keys.indexOf(item.header) != -1) {
    console.log('found it')
  } else {
    console.log('not found')
  }
})

Answer 3

我建议将some()用于此目的，例如：

keys = ['pitch1']

var y = [
  {header: 'pitch1', data: 'pitch1 data'}, 
  {header: 'pitch3', data: 'pitch3 data'}, 
  {header: 'pitch4', data: 'pitch4 data'},
  {header: 'pitch2', data: 'pitch2 data'},
  {header: 'pitch1', data: 'more pitch 1 data'},
]

var found = y.some(v => keys.includes(v.header));
if (found) {
    console.log('found it')
} else {
    console.log('not found')
}

在.map（）内的数组上使用indexOf

3 个答案: