forEach 里面的 forEach 有条件吗？

Question

I have two lists and I want to check if list B contains items from list A, so I have created a button that triggers a forEach to check if any of list B's elements' innerText is similar to the ones in list A:

    let itemsFromA = document.querySelectorAll('.itemA')
    let listB = document.getElementById('listB')

    listB.childNodes.forEach(childNodes => {
        if (childNodes.innerText === itemsFromA.forEach(itemsFromA => itemsFromA.innerText)) {
            childNodes.style.display = 'none'
        }
    })
}

But nothing happens. How can I fix this?

Thanks

Answer 1

NodeList.forEach() doesn't return anything (or always returns undefined ). Use Array.from() to convert the itemsFromA to an array, and Array.some() to check if any item has the same innerText :

let itemsFromA = document.querySelectorAll('.itemA')
let listB = document.getElementById('listB')

listB.childNodes.forEach(node => {
  if (Array.from(itemsFromA).some(itemsFromA => itemsFromA.innerText === node.innerTex)) {
    node.style.display = 'none'
  }
})

Answer 2

You can use some instead of forEach (which doesn't return anything, hence your code isn't working..).

some will test whether or not at least one element in the array passes the test implemented by the provided function.

let itemsFromA = document.querySelectorAll('.itemA')
let listB = document.getElementById('listB')

new_list = listB.childNodes.map((index, childNodes) => {
    if (itemsFromA.some(item => item.innerText === childNodes.innerText)) {
        childNodes.style.display = 'none'
    }
})

Answer 3

This is because forEach loop doesn't return values. Use map instead of forEach for expected behaviour.

eg:

if (childNodes.innerText === itemsFromA.map(itemsFromA => itemsFromA.innerText))

Answer 4

Try this way:

  let itemsFromA = document.querySelectorAll('.itemA')
  let listB = document.getElementById('listB')

  list = listB.childNodes.map((index, childNodes) => {
      itemsFromA.forEach(itemsFromA => {
        if (childNodes.innerText === itemsFromA.innerText)
           childNodes.style.display = 'none'
      })
    })
}

Answer 5

forEach does not return any value, it will only loop through the array. you should use find function instead

`let itemsFromA = document.querySelectorAll('.itemA') let listB = document.getElementById('listB')

listB.childNodes.forEach(childNode => {
    if (itemsFromA.find(itemsFromA => itemsFromA.innerText == childNode.innerText)) {
        childNodes.style.display = 'none'
    }
})

}`