How can I get this javascript function to work all of the time? (Uncaught TypeError: Cannot read pro-CodePudding

I'm trying to create two numerical inputs, each of which has their own custom ' ' and '-' buttons. However, with my current code, it appears that the button functions only work some of the time. On the other occasions I get a Uncaught TypeError: Cannot read properties of null (reading 'value') at HTMLButtonElement.<anonymous> error.

This is the HTML:

<div >
    <div >
        <div >
            <div >
                <button  data-id="one"
                    type="button"><i ></i></button>
            </div>
            <input type="number" id="one" 
                 value="0">
            <div >
                <button  data-id="one" type="button"><i
                        ></i></button>
            </div>
        </div>
    </div>

    <div >
        <div >
            <div >
                <button  data-id="two"
                    type="button"><i ></i></button>
            </div>
            <input type="number" id="two"
                 value="0">
            <div >
                <button  data-id="two" type="button"><i
                        ></i></button>
            </div>
        </div>
    </div>
</div>

And this is the Javascript:

<script>
document.addEventListener("DOMContentLoaded", () => {
    document.querySelectorAll('.minus').forEach(item => {
        item.addEventListener('click', event => {
            var input_id = event.target.getAttribute('data-id')
            console.log('Minus button clicked for input '   input_id)
            var quantityInput = document.getElementById(input_id);
            var currentQuantity = parseInt(quantityInput.value);
            quantityInput.value = currentQuantity - 1
        })
    })
    document.querySelectorAll('.plus').forEach(item => {
        item.addEventListener('click', event => {

            var input_id = event.target.getAttribute('data-id')
            console.log('Plus button clicked for input '   input_id)
            var quantityInput = document.getElementById(input_id);
            var currentQuantity = parseInt(quantityInput.value);
            quantityInput.value = currentQuantity   1
        })
    })
})

Here is a sample of the output after clicking a few of the buttons:

CodePudding user response：

The event.target may be the span inside the button, and therefore the code may not find the data-id attribute. Instead perhaps get the id without using event.target. Either use item or event.currentTarget.

CodePudding user response：

the click event happend on the <i ></i>
you may use Event.currentTarget instead of event.target

document.addEventListener("DOMContentLoaded", () =>
  {
  document.querySelectorAll('.minus').forEach(item =>
    {
    item.onclick = event => 
      {
      let
        input_id        = event.currentTarget.dataset.id
      , quantityInput   = document.getElementById(input_id)
      , currentQuantity = parseInt(quantityInput.value)
        ;
      console.log('Minus button clicked for input '   input_id)
      quantityInput.value = currentQuantity - 1
      }
    })
  document.querySelectorAll('.plus').forEach(item =>
    {
    item.onclick = event => 
      {
      let
        input_id        = event.currentTarget.dataset.id
      , quantityInput   = document.getElementById(input_id)
      , currentQuantity = parseInt(quantityInput.value)
        ;
      console.log('Plus button clicked for input '   input_id)
      quantityInput.value = currentQuantity   1
      }
    })
  })

you can also do:

document.addEventListener("DOMContentLoaded", () =>
  {
  document
    .querySelectorAll('button.minus, button.plus')
    .forEach( btn =>
    {
    btn.onclick = () => 
      {
      let
        input_id  = btn.dataset.id
      , adding    = btn.classList.contains('plus') ?  1 : -1
      , input_Qte = document.getElementById(input_id)
        ;
      input_Qte.value =  input_Qte.value   adding 
      }
    })
  })

CodePudding user response：

Replace quantityInput.value with quantityInput?.value