Drag and drop table row

Written byPhuoc Nguyen

#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`:

<!-- 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.

Questions? 🙋

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Phước Nguyễn

Drag and drop table row

#Basic setup

#Clone the table when user is moving a row

#Determine the indexes of dragging and target rows

#Demo

#See also

Questions? 🙋

Recent posts ⚡

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