Resize table columns

Suppose we want to adjust the size of any column in the following table ：

<table id="resizeMe" class="table">
    ...
</table>

Prepare the adjuster

For each column , Let's insert a div Elements , Indicates that related columns can be resized . The resizing element is absolutely inside the column . Their CSS The style is as follows ：

.table th {
    position: relative;
}
.resizer {
    /* Displayed at the right side of column */
    position: absolute;
    top: 0;
    right: 0;
    width: 5px;
    cursor: col-resize;
    user-select: none;
}

want establish Resize And will They are attached to columns , We have to Inquire about and Traverse All columns ：

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

// Query all headers
const cols = table.querySelectorAll('th');

// Loop over them
[].forEach.call(cols, function (col) {
    // Create a resizer element
    const resizer = document.createElement('div');
    resizer.classList.add('resizer');

    // Set the height
    resizer.style.height = `${table.offsetHeight}px`;

    // Add a resizer element to the column
    col.appendChild(resizer);

    // Will be implemented in the next section
    createResizableColumn(col, resizer);
});

Handle resizing events

We will implement a function ,createResizableColumn, It takes two arguments ：

• col Indicates the header
• resizer Represents the resizing element in the column

To allow users to resize col, We have to deal with three events ：

• mousedown On the adjuster ： Track the current position of the mouse
• mousemoveon document： Calculate how far the mouse has moved , And adjust the column width
• mouseupon document： Deleted event handler document

const createResizableColumn = function (col, resizer) {
    // Track the current position of mouse
    let x = 0;
    let w = 0;

    const mouseDownHandler = function (e) {
        // Get the current mouse position
        x = e.clientX;

        // Calculate the current width of column
        const styles = window.getComputedStyle(col);
        w = parseInt(styles.width, 10);

        // Attach listeners for document's events
        document.addEventListener('mousemove', mouseMoveHandler);
        document.addEventListener('mouseup', mouseUpHandler);
    };

    const mouseMoveHandler = function (e) {
        // Determine how far the mouse has been moved
        const dx = e.clientX - x;

        // Update the width of column
        col.style.width = `${w + dx}px`;
    };

    // When user releases the mouse, remove the existing event listeners
    const mouseUpHandler = function () {
        document.removeEventListener('mousemove', mouseMoveHandler);
        document.removeEventListener('mouseup', mouseUpHandler);
    };

    resizer.addEventListener('mousedown', mouseDownHandler);
};

Highlight the adjuster

We can slightly improve the user experience . When the user hovers or clicks to resize , You can highlight it . In order to show this idea in the simplest way , We give :hover The selector adds a solid border ：

.resizer:hover,
.resizing {
    border-right: 2px solid blue;
}

When resizing When the user clicks and drags the adjuster , This class is added to the adjuster ：

const mouseDownHandler = function(e) {
    ...
    resizer.classList.add('resizing');
};

const mouseUpHandler = function() {
    ...
    resizer.classList.remove('resizing');
};