JSFiddle - React, Tailwind, and code Playground

by Plippie Plop

HTML

<div id="container">
    <div id="left_panel"> left content! </div>
    <div id="right_panel">
        <div id="drag"></div> right content!
    </div>
</div>

CSS

body, html {
    width: 100%;
    height: 100%;
    margin: 0;
    padding: 0;
}
#container {
    width: 100%;
    height: 100%;
    
}
 #left_panel {
    position: absolute;
    left: 0;
    top: 0;
    bottom: 0;
    right: 100px;
    background: grey;
}

#right_panel {
    position: absolute;
    right: 0;
    top: 0;
    bottom: 0;
    width: 200px;
    color:#fff;
    background: black;
}
 #drag {
    position: absolute;
    left: -4px;
    top: 0;
    bottom: 0;
    width: 8px;
    cursor: w-resize;
}

JavaScript

var isResizing = false,
    lastDownX = 0;

$(function () {
    var container = $('#container'),
        left = $('#left_panel'),
        right = $('#right_panel'),
        handle = $('#drag');

    handle.on('mousedown', function (e) {
        isResizing = true;
        lastDownX = e.clientX;
    });

    $(document).on('mousemove', function (e) {
        // we don't want to do anything if we aren't resizing.
        if (!isResizing) 
            return;
        
        var offsetRight = container.width() - (e.clientX - container.offset().left);

        left.css('right', offsetRight);
        right.css('width', offsetRight);
    }).on('mouseup', function (e) {
        // stop resizing
        isResizing = false;
    });
});