Question 199067 in Javascript Question posted in
A very good W3school tutorial can be found here.

Javascript – Items order after drag and drop swap

I am doing a project where images in a 3×3 grid are re-arranged by drag and drop.
When an image is dragged and dropped over another, they swap positions and I have got that part working, but I also need a line of text at the bottom showing how the images have been re-ordered. So if I swap the items 1 and 5 the text would no longer read: 1,2,3,4,5,6,7,8,9 but instead it should look like: 5,2,3,4,1,6,7,8,9.

I am really struggling with how to print the new numbers order after the items swap. Here is how it looks (the colors of the boxes were chosen randomly and have no importance):

Image re-ordering

This is my code:

//IMAGE ORDER

let order = [1, 2, 3, 4, 5, 6, 7, 8, 9]

function showOrder(order) {
  document.getElementById('order').textContent = "Order: " + order.toString();
}

showOrder(order);

//DRAG AND DROP SWAP

var draggedImage = null;
var items;

function dragStart(e) {
  draggedImage = this;
  e.dataTransfer.effectAllowed = "move";
  e.dataTransfer.setData("item", this.innerHTML);
}

function dragOver(e) {
  e.preventDefault();

  e.dataTransfer.dropEffect = "move";
  return false;
}

function dragEnter(e) {
  this.classList.add("dragover");
}

function dragLeave(e) {
  this.classList.remove("dragover");
}

function drop(e) {
  e.stopPropagation();

  if (draggedImage != this) {
    draggedImage.innerHTML = this.innerHTML;
    draggedImage.setAttribute("data-item", this.innerHTML);

    let replacedImage = e.dataTransfer.getData("item");
    this.innerHTML = replacedImage;
    this.setAttribute("data-item", replacedImage);
  }
  return false;
}

function dragEnd(e) {
  items.forEach(function(item) {
    item.classList.remove("dragover");
  });
}

document.addEventListener("DOMContentLoaded", event => {
  items = document.querySelectorAll(".container .image");

  items.forEach(function(item) {
    item.addEventListener("dragstart", dragStart);
    item.addEventListener("dragenter", dragEnter);
    item.addEventListener("dragover", dragOver);
    item.addEventListener("dragleave", dragLeave);
    item.addEventListener("drop", drop);
    item.addEventListener("dragend", dragEnd);
  });

});
.container {
  width: 330px;
  height: 330px;
  background-color: lightgrey;
  display: flex;
  flex-wrap: wrap;
}

.image {
  width: 100px;
  height: 100px;
  background-color: #fff5d7;
  text-align: center;
  line-height: 100px;
  margin: 5px;
  cursor: move;
}

.order {
  width: 330px;
  height: 50px;
  background-color: lightgrey;
  margin-top: 10px;
  text-align: center;
  line-height: 50px;
  font-size: x-large;
  font-family: Helvetica;
}
<div class="container">
  <div draggable="true" class="image" id="1"><img src="Dummy billeder/nummer 1.png" width="100px"></div>
  <div draggable="true" class="image" id="2"><img src="Dummy billeder/nummer 2.png" width="100px"></div>
  <div draggable="true" class="image" id="3"><img src="Dummy billeder/nummer 3.png" width="100px"></div>
  <div draggable="true" class="image" id="4"><img src="Dummy billeder/nummer 4.png" width="100px"></div>
  <div draggable="true" class="image" id="5"><img src="Dummy billeder/nummer 5.png" width="100px"></div>
  <div draggable="true" class="image" id="6"><img src="Dummy billeder/nummer 6.png" width="100px"></div>
  <div draggable="true" class="image" id="7"><img src="Dummy billeder/nummer 7.png" width="100px"></div>
  <div draggable="true" class="image" id="8"><img src="Dummy billeder/nummer 8.png" width="100px"></div>
  <div draggable="true" class="image" id="9"><img src="Dummy billeder/nummer 9.png" width="100px"></div>
</div>

<div id="order"></div>

I have tried finding a way to indentify the position of the two images in the grid and then swapping those numbers in an array, when an image is dropped but I could not get it to work.

Tags:

2

Answers


  1. 0

    Copy the IDs to your draggable content () and update the order box on the drop.

    document.querySelectorAll('.container .image').forEach(div => {
  div.querySelector('img').dataset.id = div.id;
});

const updateOrder = () => {
  document.getElementById('order').textContent = 'Order: ' + 
    [...document.querySelectorAll('.container .image img')].map(img => img.dataset.id).join(', ');
};

updateOrder();

//DRAG AND DROP SWAP

var draggedImage = null;
var items;

function dragStart(e) {
    draggedImage = this;
    e.dataTransfer.effectAllowed="move";
    e.dataTransfer.setData("item", this.innerHTML); 
}

function dragOver(e) {
    e.preventDefault();

    e.dataTransfer.dropEffect = "move";
    return false;
}

function dragEnter(e) {
    this.classList.add("dragover"); 
}

function dragLeave(e) {
    this.classList.remove("dragover"); 
}

function drop(e) {
    e.stopPropagation();

    if (draggedImage != this) {
        draggedImage.innerHTML = this.innerHTML; 
        draggedImage.setAttribute("data-item", this.innerHTML);

        let replacedImage = e.dataTransfer.getData("item"); 
        this.innerHTML = replacedImage;
        this.setAttribute("data-item", replacedImage);
        updateOrder();
        }
        return false;
}

function dragEnd(e) {
    items.forEach(function(item) {
        item.classList.remove("dragover"); 
    });
}

document.addEventListener("DOMContentLoaded", event => {
    items = document.querySelectorAll(".container .image");

    items.forEach(function(item) {
        item.addEventListener("dragstart", dragStart);
        item.addEventListener("dragenter", dragEnter);
        item.addEventListener("dragover", dragOver);
        item.addEventListener("dragleave", dragLeave);
        item.addEventListener("drop", drop);
        item.addEventListener("dragend", dragEnd);
    });
});
    <!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>My Website</title>
    <link rel="stylesheet" href="./style.css">
    <link rel="icon" href="./favicon.ico" type="image/x-icon">
    <style>
      .container {
          width: 330px;
          height: 330px;
          background-color: lightgrey;
          display: flex;
          flex-wrap: wrap;
      }
      .image {
        width: 100px;
        height: 100px;
        background-color: #fff5d7;
        text-align: center;
        line-height: 100px;
        margin: 5px;
        cursor: move;
      }
      .order {
        width: 330px;
        height: 50px;
        background-color: lightgrey;
        margin-top: 10px;
        text-align: center;
        line-height: 50px;
        font-size:x-large;
        font-family: Helvetica;
      }
  </style>
  </head>
  <body>
        <h1>Image re-ordering</h1>  
        <h2>Drag and drop to swap images</h2>
        <div class="container">
          <div draggable="true" class="image" id="1"><img src="Dummy billeder/nummer 1.png" width="100px"></div>
          <div draggable="true" class="image" id="2"><img src="Dummy billeder/nummer 2.png" width="100px"></div>
          <div draggable="true" class="image" id="3"><img src="Dummy billeder/nummer 3.png" width="100px"></div>
          <div draggable="true" class="image" id="4"><img src="Dummy billeder/nummer 4.png" width="100px"></div>
          <div draggable="true" class="image" id="5"><img src="Dummy billeder/nummer 5.png" width="100px"></div>
          <div draggable="true" class="image" id="6"><img src="Dummy billeder/nummer 6.png" width="100px"></div>
          <div draggable="true" class="image" id="7"><img src="Dummy billeder/nummer 7.png" width="100px"></div>
          <div draggable="true" class="image" id="8"><img src="Dummy billeder/nummer 8.png" width="100px"></div>
          <div draggable="true" class="image" id="9"><img src="Dummy billeder/nummer 9.png" width="100px"></div>
        </div>
        <div class="order" id="order"></div>
    <script src="gasflasker test.js"></script>
  </body>
</html>

    But a better approach would be to move the whole boxes:

    const $container = document.querySelector('.container');

const updateOrder = () => {
  document.getElementById('order').textContent = 'Order: ' + 
    [...document.querySelectorAll('.container .image')].map(img => img.id).join(', ');
};

updateOrder();

//DRAG AND DROP SWAP

var draggedImage = null;
var items;

function dragStart(e) {
    draggedImage = this;
    e.dataTransfer.effectAllowed="move";
}

function dragOver(e) {
    e.preventDefault();
    e.dataTransfer.dropEffect = "move";
    return false;
}

function dragEnter(e) {
    this.classList.add("dragover"); 
}

function dragLeave(e) {
    this.classList.remove("dragover"); 
}

function drop(e) {
    e.stopPropagation();

    if (draggedImage != this) {
        const span = document.createElement('span');
        $container.insertBefore(span, draggedImage);
        $container.insertBefore(draggedImage, this.nextSibling);
        $container.insertBefore(this, span);
        span.remove();
        updateOrder();
    }
}

function dragEnd(e) {
    items.forEach(function(item) {
        item.classList.remove("dragover"); 
    });
}

document.addEventListener("DOMContentLoaded", event => {
    items = document.querySelectorAll(".container .image");

    items.forEach(function(item) {
        item.addEventListener("dragstart", dragStart);
        item.addEventListener("dragenter", dragEnter);
        item.addEventListener("dragover", dragOver);
        item.addEventListener("dragleave", dragLeave);
        item.addEventListener("drop", drop);
        item.addEventListener("dragend", dragEnd);
    });
});
    <!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>My Website</title>
    <link rel="stylesheet" href="./style.css">
    <link rel="icon" href="./favicon.ico" type="image/x-icon">
    <style>
      .container {
          width: 330px;
          height: 330px;
          background-color: lightgrey;
          display: flex;
          flex-wrap: wrap;
      }
      .image {
        width: 100px;
        height: 100px;
        background-color: #fff5d7;
        text-align: center;
        line-height: 100px;
        margin: 5px;
        cursor: move;
      }
      .order {
        width: 330px;
        height: 50px;
        background-color: lightgrey;
        margin-top: 10px;
        text-align: center;
        line-height: 50px;
        font-size:x-large;
        font-family: Helvetica;
      }
  </style>
  </head>
  <body>
        <h1>Image re-ordering</h1>  
        <h2>Drag and drop to swap images</h2>
        <div class="container">
          <div draggable="true" class="image" id="1"><img src="Dummy billeder/nummer 1.png" width="100px"></div>
          <div draggable="true" class="image" id="2"><img src="Dummy billeder/nummer 2.png" width="100px"></div>
          <div draggable="true" class="image" id="3"><img src="Dummy billeder/nummer 3.png" width="100px"></div>
          <div draggable="true" class="image" id="4"><img src="Dummy billeder/nummer 4.png" width="100px"></div>
          <div draggable="true" class="image" id="5"><img src="Dummy billeder/nummer 5.png" width="100px"></div>
          <div draggable="true" class="image" id="6"><img src="Dummy billeder/nummer 6.png" width="100px"></div>
          <div draggable="true" class="image" id="7"><img src="Dummy billeder/nummer 7.png" width="100px"></div>
          <div draggable="true" class="image" id="8"><img src="Dummy billeder/nummer 8.png" width="100px"></div>
          <div draggable="true" class="image" id="9"><img src="Dummy billeder/nummer 9.png" width="100px"></div>
        </div>
        <div class="order" id="order"></div>
    <script src="gasflasker test.js"></script>
  </body>
</html>

    If you want to go really cool, here’s a reactive approach without manipulating DOM manually:

    const $container = document.querySelector('.container');

let updatePromise;

const ids = new Proxy([], {
  set(target, prop, val){
    // postpone the update with a microtask
    updatePromise ??= Promise.resolve().then(() => {
      updatePromise = null;
      document.getElementById('order').textContent = 'Order: ' + 
    target.join(', ');
      target.forEach(id => {
        $container.appendChild(document.getElementById(id));
      });
    });
    return Reflect.set(target, prop, val);
  }
});


ids.push(...[...document.querySelectorAll('.container .image')].map(img => img.id));

//DRAG AND DROP SWAP

var draggedImageId;
var items;

function dragStart(e) {
    draggedImageId = this.id;
    e.dataTransfer.effectAllowed="move";
}

function dragOver(e) {
    e.preventDefault();
    e.dataTransfer.dropEffect = "move";
    return false;
}

function dragEnter(e) {
    this.classList.add("dragover"); 
}

function dragLeave(e) {
    this.classList.remove("dragover"); 
}

function drop(e) {
    e.stopPropagation();

    if (draggedImageId !== this.id) {
        const [from, to] = [ids.indexOf(draggedImageId), ids.indexOf(this.id)];
        [ids[from], ids[to]] = [ids[to], ids[from]];
    }
}

function dragEnd(e) {
    items.forEach(function(item) {
        item.classList.remove("dragover"); 
    });
}

document.addEventListener("DOMContentLoaded", event => {
    items = document.querySelectorAll(".container .image");

    items.forEach(function(item) {
        item.addEventListener("dragstart", dragStart);
        item.addEventListener("dragenter", dragEnter);
        item.addEventListener("dragover", dragOver);
        item.addEventListener("dragleave", dragLeave);
        item.addEventListener("drop", drop);
        item.addEventListener("dragend", dragEnd);
    });
});
    <!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>My Website</title>
    <link rel="stylesheet" href="./style.css">
    <link rel="icon" href="./favicon.ico" type="image/x-icon">
    <style>
      .container {
          width: 330px;
          height: 330px;
          background-color: lightgrey;
          display: flex;
          flex-wrap: wrap;
      }
      .image {
        width: 100px;
        height: 100px;
        background-color: #fff5d7;
        text-align: center;
        line-height: 100px;
        margin: 5px;
        cursor: move;
      }
      .order {
        width: 330px;
        height: 50px;
        background-color: lightgrey;
        margin-top: 10px;
        text-align: center;
        line-height: 50px;
        font-size:x-large;
        font-family: Helvetica;
      }
  </style>
  </head>
  <body>
        <h1>Image re-ordering</h1>  
        <h2>Drag and drop to swap images</h2>
        <div class="container">
          <div draggable="true" class="image" id="1"><img src="Dummy billeder/nummer 1.png" width="100px"></div>
          <div draggable="true" class="image" id="2"><img src="Dummy billeder/nummer 2.png" width="100px"></div>
          <div draggable="true" class="image" id="3"><img src="Dummy billeder/nummer 3.png" width="100px"></div>
          <div draggable="true" class="image" id="4"><img src="Dummy billeder/nummer 4.png" width="100px"></div>
          <div draggable="true" class="image" id="5"><img src="Dummy billeder/nummer 5.png" width="100px"></div>
          <div draggable="true" class="image" id="6"><img src="Dummy billeder/nummer 6.png" width="100px"></div>
          <div draggable="true" class="image" id="7"><img src="Dummy billeder/nummer 7.png" width="100px"></div>
          <div draggable="true" class="image" id="8"><img src="Dummy billeder/nummer 8.png" width="100px"></div>
          <div draggable="true" class="image" id="9"><img src="Dummy billeder/nummer 9.png" width="100px"></div>
        </div>
        <div class="order" id="order"></div>
    <script src="gasflasker test.js"></script>
  </body>
</html>
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  2. 0

    Here’s a simpler and cleaner example/suggestion in where:

    • Store index in data atrribute
    • Retrieve the indexes of the dragged and target drop elements
    • Swap the elements in the DOM
    • Update the array given those two indexes
    • Print the order array
    • Use delegated events (assigned on the wrapper .grid element)
    const elGrid = document.querySelector(".grid");
const elOrder = document.querySelector("#order");
const order = [...elGrid.children].map(el => el.dataset.index);
let elDrag;

const showOrder = () => elOrder.textContent = `Order: ${order}`;

const events = {
  dragstart() { elDrag = this; },
  dragover(ev) { ev.preventDefault(); },
  drop() {
    if (elDrag === this) return;
    const ia = [...elGrid.children].indexOf(elDrag);
    const ib = [...elGrid.children].indexOf(this);
    elDrag.replaceWith(this.cloneNode(true));
    this.replaceWith(elDrag);
    [order[ia], order[ib]] = [order[ib], order[ia]];
    showOrder();
  }
};

[...elGrid.children].forEach((el, i) => el.draggable = true);
["dragstart", "dragover", "drop"].forEach(evName => {
  elGrid.addEventListener(evName, (ev) => {
    const elItem = ev.target.closest(".item");
    if (!elItem) return; 
    events[evName].call(elItem, ev);
  });
});
showOrder();
    .grid {
  display: inline-grid;
  grid-template-columns: repeat(3, 1fr);
  background-color: #d3d3d3;
  gap: 0.3rem;
  padding: 0.3rem;
}

.item {
  display: inline-flex;
  background-color: #fffac2;
  padding: 0.3rem;
}
    <div class="grid">
  <div class="item" data-index="1"><img src="https://placehold.co/40x40/0bf/fff?text=1" alt="1"></div>
  <div class="item" data-index="2"><img src="https://placehold.co/40x40/0fb/fff?text=2" alt="2"></div>
  <div class="item" data-index="3"><img src="https://placehold.co/40x40/bf0/fff?text=3" alt="3"></div>
  <div class="item" data-index="4"><img src="https://placehold.co/40x40/b0f/fff?text=4" alt="4"></div>
  <div class="item" data-index="5"><img src="https://placehold.co/40x40/fb0/fff?text=5" alt="5"></div>
  <div class="item" data-index="6"><img src="https://placehold.co/40x40/f0b/fff?text=6" alt="6"></div>
  <div class="item" data-index="7"><img src="https://placehold.co/40x40/8f0/fff?text=7" alt="7"></div>
  <div class="item" data-index="8"><img src="https://placehold.co/40x40/f80/fff?text=8" alt="8"></div>
  <div class="item" data-index="9"><img src="https://placehold.co/40x40/08f/fff?text=9" alt="9"></div>
</div>

<div id="order"></div>
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