Increment and update value in the total number after insert new rows dynamically

Question

EDIT: I have updated the code with the answers.

I have a increment function that is working fine. However:

1. I would like to set some limits based on the total number available in one of the span. For example, 10. So the incrementing can't be more than 10. #DONE

2. Another issue is that I am planning to have multiple rows and before I save I want to make sure if we count the increments in every row it should not be more than 10 as well. If it decrease the total number (span) dynamically would be nice.

I'm adding rows dynamically with the ADD button, how can I add news rows that actually work with the current functions? Mine rows just clone the first one and the increment function is disabled.

document.addEventListener('DOMContentLoaded', async function() {
  document.querySelector('#addlocationdest').addEventListener('click', add);
});
function add() {
    var x = 1;
    var container = document.getElementById('destination');
    var detail = document.getElementById('row');
    var clone = detail.cloneNode(true);
    clone.id = "destination" + x;
    x++;
    container.appendChild(clone);

}

window.addEventListener("load", () => {
  let elTotalQuantity = document.querySelector("#totalqty");
  let totalQuantity = parseInt(elTotalQuantity.innerHTML);
  
  function getSumOfRows() {
    let sum = 0;
    for (let input of document.querySelectorAll("form .row > input.quantity"))
      sum += parseInt(input.value);
    return sum;
  }
  
  for (let row of document.querySelectorAll("form .row")) {
    let input = row.querySelector("input");
    row.querySelector(".increment").addEventListener("click", () => {
      if (getSumOfRows() >= totalQuantity) return;
      input.value++;
      elTotalQuantity.innerHTML = totalQuantity - getSumOfRows();
    });
    row.querySelector(".decrement").addEventListener("click", () => {
      if (input.value <= 0) return;
      input.value--;
      elTotalQuantity.innerHTML = totalQuantity - getSumOfRows();
    });
  }
});

<div id="location" class="hide">
                    <div class="title">Transfer details</div><br>
                    <div class="line padded-s">Total Quantity: <span>10</span></div>
                    <br>
                        <form>
                            <label>New Total Quantity at this location: <span id="totalqty">10</span></label>
                            <br>
                            <div id="destination">
                                <div id="row" class="row">
                                    <button type="button" class="decrement">-</button>
                                    <input type="text" class="quantity" value="0" readonly/>
                                    <button type="button" class="increment">+</button>
                                    <a>Location: </a>
                                    <input type="text" class="location" value="0" readonly/>
                                </div>
                            </div>
                        </form>

                        <label>Total being transfer: <p id="total-sum"></p></label>
                        <br>
                        <button type="button" id="addlocationdest">ADD</button>
            <button type="button" id="removelocationdest">REMOVE</button>
                </div>

Answer 1

Prologue
As long as the total quantity is fixed at the beginning of the script-execution, this works. Otherwise, it would be best to save the actual allowed total quantity as an attribute, and observe it using a MutationObserver. That way you can update your max. value in your code dynamically, when the total quantity-attribute changes. You can define custom attributes by naming them "data-*" where "*" is a custom name.

Solution for your problem
You are using the same ID on multiple elements. What you meant were classes, so change id="increment" to class="increment", and the same for decrement.

Since we don't want to input something with the buttons, but add listener to them, I'd say it is better to actually use <button>. In forms, buttons act as type="submit", which we don't want, so we need to change it to type="button".

Since the rows and the total quantity actually belong together, it is wiser to place them together into one <form>-element. However, you can still group the buttons and inputs as a row together using <div>.

Now regarding the in-/decrementing of the row's values and the total quantity:

1. Save the allowed total quantity in a variable
2. Add event-listener to the corresponding buttons
3. If action is valid, change row's value
4. Update total quantity number to totalQuantity - getSumOfRows()

To add new rows dynamically, we create and setup such an element, and append it to the form. See the appendNewRow()-function below.

Sidenote
I have added the readonly attribute to the input-fields so that you cannot enter numbers via keyboard.

window.addEventListener("load", () => {
  let elTotalQuantity = document.querySelector("#totalqty");
  let totalQuantity = parseInt(elTotalQuantity.innerHTML);
  
  function getSumOfRows() {
    let sum = 0;
    for (let input of document.querySelectorAll("form .row > input.quantity"))
      sum += parseInt(input.value);
    return sum;
  }
  function updateTotalQuantity() {
      elTotalQuantity.innerHTML = totalQuantity - getSumOfRows();
  }
  
  function appendNewRow() {
    let row = document.createElement("div");
    row.classList.add("row");
    let child;
    
    // input.quantity
    let input = document.createElement("input");
    input.classList.add("quantity");
    input.value = "0";
    input.setAttribute("readonly", "");
    input.setAttribute("type", "text");
    row.append(input);
    
    // button.increment
    child = document.createElement("button");
    child.classList.add("increment");
    child.innerHTML = "+";
    child.setAttribute("type", "button");
    child.addEventListener("click", () => {
      if (getSumOfRows() >= totalQuantity) return;
      input.value++;
      updateTotalQuantity();
    });
    row.append(child);
    
    // button.increment
    child = document.createElement("button");
    child.classList.add("decrement");
    child.innerHTML = "-";
    child.setAttribute("type", "button");
    child.addEventListener("click", () => {
      if (input.value <= 0) return;
      input.value--;
      updateTotalQuantity();
    });
    row.append(child);
    
    // button.remove-row
    child = document.createElement("button");
    child.classList.add("remove-row");
    child.innerHTML = "Remove";
    child.setAttribute("type", "button");
    child.addEventListener("click", () => {
      row.remove();
      updateTotalQuantity();
    });
    row.append(child);
    
    document.querySelector("form .rows").append(row);
  }
  
  document.querySelector("form .add-row").addEventListener("click", () => appendNewRow());
  
  appendNewRow();
});

<form>
  <label>Total Quantity: <span id="totalqty">10</span></label>
  <br>
  <div class="rows">
  </div>
  <button type="button" class="add-row">Add new row</button>
</form>

Answer 2

QuerySelector only selects the first occurrence so you haven't really added a listener to the second "row". You should use querySelectorAll but, instead of unique ids, use classes.

<input class="increment" type="button" value="+" />

1. Now you can use document.querySelectorAll(".increment") to get all elements in an array.

2. You can traverse in the DOM by using parentElement. By knowing which button you clicked, you can traverse up to the form element and then select the first child - which is an input. A more dynamic way would be to use querySelector to select the input, in case the HTML change in the future. Anyway, that's how you can know which input to manipulate based on where the buttons are in the DOM.

3. I added two global variables, totalSum and maxSum. maxSum is fetched from your span element (which I assigned an unique id to). totalSum makes sure that all inputs combined doesn't exceed maxSum.

4. You had some duplicate code, so I refactored it into a new method: changeValue.

In all, I think the code speaks for itself.

Oh, this code doesn't take into account that the user can change the value inside the input. I will leave that for you to figure out with an "oninput" listener on each text input.

var totalSum = 0;  // 3
var maxSum = 0
var totalSumElement = null;

document.addEventListener('DOMContentLoaded', async function() {
  totalSumElement = document.getElementById('total-sum');
  maxSum = document.getElementById('max-sum').innerText;

  var incrementElements = document.querySelectorAll('.increment');  // 1
  var decrementElements = document.querySelectorAll('.decrement');

  addListener('click', incrementElements, incrementValue);
  addListener('click', decrementElements, decrementValue);
});


function addListener(type, elementArr, func) {
  for (element of elementArr) {
    element.addEventListener(type, func);
  }
}

function withinRange(newValue) {
  var maxReached  = newValue > maxSum;  // 3
  var zeroReached = newValue < 0;

  return !maxReached && !zeroReached;
}

function changeValue(event, change) {  // 4
  if (withinRange(totalSum + change)) {
    let parent = event.currentTarget.parentElement;  // 2
    let input  = parent.children[0];
    let value  = parseInt(input.value) || 0;
    
    if (withinRange(value + change)) {
      input.value = value + change;
      totalSum = totalSum + change;
    }
  }

  totalSumElement.textContent = `Total: ${totalSum}`;
}

function incrementValue(event) {
  changeValue(event, 1);
}

function decrementValue(event) {
  changeValue(event, -1);
}

#totalqty {
  padding-bottom: 1rem;
}

<div id="totalqty" class="line padded-s">Total Quantity: <span id="max-sum">10</span></div>

<form>
  <input type="text" value="0" />
  <input class="increment" type="button" value="+" />
  <input class="decrement" type="button" value="-" />
</form>
<form>
  <input type="text" value="0" />
  <input class="increment" type="button" value="+" />
  <input class="decrement" type="button" value="-" />
</form>

<p id="total-sum"></p>