← Back toHTML DOM

Drag and drop table row

Written byPhuoc Nguyen

Created

02 Apr, 2020

Last updated

07 May, 2021

#Basic setup

As mentioned in the Drag and drop element in a list example, we need handle three events:

`mousedown` for the first cell of any row, so user can click and drag the first cell in each row
`mousemove` for `document`: This event triggers when user moves the row around, and we will create and insert a placeholder row depending on the direction (up or down)
`mouseup` for `document`: This event occurs when user drags the row.

Here is the skeleton of these event handlers:

// Query the table
const table = document.getElementById('table');

const mouseDownHandler = function(e) {
    ...

    // Attach the listeners to `document`
    document.addEventListener('mousemove', mouseMoveHandler);
    document.addEventListener('mouseup', mouseUpHandler);
};

const mouseMoveHandler = function(e) {
    ...
};

const mouseUpHandler = function() {
    ...
    // Remove the handlers of `mousemove` and `mouseup`
    document.removeEventListener('mousemove', mouseMoveHandler);
    document.removeEventListener('mouseup', mouseUpHandler);
};

// Query all rows
table.querySelectorAll('tr').forEach(function(row, index) {
    // Ignore the header
    // We don't want user to change the order of header
    if (index === 0) {
        return;
    }

    // Get the first cell of row
    const firstCell = row.firstElementChild;
    firstCell.classList.add('draggable');

    // Attach event handler
    firstCell.addEventListener('mousedown', mouseDownHandler);
});

#Clone the table when user is moving a row

Since this task is performed once, we need a flag to track if it's executed:

let isDraggingStarted = false;

const mouseMoveHandler = function(e) {
    if (!isDraggingStarted) {
        isDraggingStarted = true;

        cloneTable();
    }
    ...
};

`cloneTable` creates an element that has the same position as the table, and is shown right before the table:

let list;

const cloneTable = function () {
    // Get the bounding rectangle of table
    const rect = table.getBoundingClientRect();

    // Get the width of table
    const width = parseInt(window.getComputedStyle(table).width);

    // Create new element
    list = document.createElement('div');

    // Set the same position as table
    list.style.position = 'absolute';
    list.style.left = `${rect.left}px`;
    list.style.top = `${rect.top}px`;

    // Insert it before the table
    table.parentNode.insertBefore(list, table);

    // Hide the table
    table.style.visibility = 'hidden';
};

Imagine that `list` consists of items which are cloned from the table rows:

const cloneTable = function() {
    ...

    // Loop over the rows
    table.querySelectorAll('tr').forEach(function(row) {
        const item = document.createElement('div');

        const newTable = document.createElement('table');
        const newRow = document.createElement('tr');

        // Query the cells of row
        const cells = [].slice.call(row.children);
        cells.forEach(function(cell) {
            const newCell = cell.cloneNode(true);
            newRow.appendChild(newCell);
        });

        newTable.appendChild(newRow);
        item.appendChild(newTable);

        list.appendChild(item);
    });
};

After this step, we have the following `list`:

html

<!-- The list -->
<div>
    <!-- First item -->
    <div>
        <table>
            <!-- The first row of original table -->
            <tr>
                ...
            </tr>
        </table>
    </div>

    <!-- Second item -->
    <div>
        <table>
            <!-- The second row of original table -->
            <tr>
                ...
            </tr>
        </table>
    </div>

    <!-- ... -->
</div>

<!-- The original table -->
<table>
    ...
</table>

It's worth noting that when cloning cells in each item, we have to set the cell width same as the original cell. So the item looks like the original row completely:

cells.forEach(function (cell) {
    const newCell = cell.cloneNode(true);
    // Set the width as the original cell
    newCell.style.width = `${parseInt(window.getComputedStyle(cell).width)}px`;
    newRow.appendChild(newCell);
});

#Determine the indexes of dragging and target rows

let draggingEle; // The dragging element
let draggingRowIndex; // The index of dragging row

const mouseDownHandler = function (e) {
    // Get the original row
    const originalRow = e.target.parentNode;
    draggingRowIndex = [].slice.call(table.querySelectorAll('tr')).indexOf(originalRow);
};

const mouseMoveHandler = function (e) {
    if (!isDraggingStarted) {
        cloneTable();

        // Query the dragging element
        draggingEle = [].slice.call(list.children)[draggingRowIndex];
    }
};

const mouseUpHandler = function () {
    // Get the end index
    const endRowIndex = [].slice.call(list.children).indexOf(draggingEle);
};

As we have `draggingRowIndex` and `endRowIndex`, it's now easy to check if user drops to the top or bottom of table. And we can decide how to move the target row before or after the dragging row:

const mouseUpHandler = function () {
    // Move the dragged row to `endRowIndex`
    let rows = [].slice.call(table.querySelectorAll('tr'));
    draggingRowIndex > endRowIndex
        ? // User drops to the top
          rows[endRowIndex].parentNode.insertBefore(rows[draggingRowIndex], rows[endRowIndex])
        : // User drops to the bottom
          rows[endRowIndex].parentNode.insertBefore(rows[draggingRowIndex], rows[endRowIndex].nextSibling);
};

Following is the final demo. Try to drag and drop the first cell of any row.

#See also

If you found this post helpful, please consider giving the repository a star on GitHub or sharing the post on your favorite social networks 😍. Your support would mean a lot to me!

Questions? 🙋

Do you have any questions about front-end development? If so, feel free to create a new issue on GitHub using the button below. I'm happy to help with any topic you'd like to learn more about, even beyond what's covered in this post.

While I have a long list of upcoming topics, I'm always eager to prioritize your questions and ideas for future content. Let's learn and grow together! Sharing knowledge is the best way to elevate ourselves 🥷.

Ask me questions

Newsletter 🔔

If you're into front-end technologies and you want to see more of the content I'm creating, then you might want to consider subscribing to my newsletter.

By subscribing, you'll be the first to know about new articles, products, and exclusive promotions.

Don't worry, I won't spam you. And if you ever change your mind, you can unsubscribe at any time.

Phước Nguyễn