How to detect DIV's dimension changed?

Question

I\'ve the following sample html, there is a DIV which has 100% width. It contains some elements. While performing windows re-sizing, the inner elements may be re-positioned,

Answer 1

ResizeSensor.js is part of a huge library, but I reduced its functionality to THIS:

function ResizeSensor(element, callback)
{
    let zIndex = parseInt(getComputedStyle(element));
    if(isNaN(zIndex)) { zIndex = 0; };
    zIndex--;

    let expand = document.createElement('div');
    expand.style.position = "absolute";
    expand.style.left = "0px";
    expand.style.top = "0px";
    expand.style.right = "0px";
    expand.style.bottom = "0px";
    expand.style.overflow = "hidden";
    expand.style.zIndex = zIndex;
    expand.style.visibility = "hidden";

    let expandChild = document.createElement('div');
    expandChild.style.position = "absolute";
    expandChild.style.left = "0px";
    expandChild.style.top = "0px";
    expandChild.style.width = "10000000px";
    expandChild.style.height = "10000000px";
    expand.appendChild(expandChild);

    let shrink = document.createElement('div');
    shrink.style.position = "absolute";
    shrink.style.left = "0px";
    shrink.style.top = "0px";
    shrink.style.right = "0px";
    shrink.style.bottom = "0px";
    shrink.style.overflow = "hidden";
    shrink.style.zIndex = zIndex;
    shrink.style.visibility = "hidden";

    let shrinkChild = document.createElement('div');
    shrinkChild.style.position = "absolute";
    shrinkChild.style.left = "0px";
    shrinkChild.style.top = "0px";
    shrinkChild.style.width = "200%";
    shrinkChild.style.height = "200%";
    shrink.appendChild(shrinkChild);

    element.appendChild(expand);
    element.appendChild(shrink);

    function setScroll()
    {
        expand.scrollLeft = 10000000;
        expand.scrollTop = 10000000;

        shrink.scrollLeft = 10000000;
        shrink.scrollTop = 10000000;
    };
    setScroll();

    let size = element.getBoundingClientRect();

    let currentWidth = size.width;
    let currentHeight = size.height;

    let onScroll = function()
    {
        let size = element.getBoundingClientRect();

        let newWidth = size.width;
        let newHeight = size.height;

        if(newWidth != currentWidth || newHeight != currentHeight)
        {
            currentWidth = newWidth;
            currentHeight = newHeight;

            callback();
        }

        setScroll();
    };

    expand.addEventListener('scroll', onScroll);
    shrink.addEventListener('scroll', onScroll);
};

How to use it:

let container = document.querySelector(".container");
new ResizeSensor(container, function()
{
    console.log("dimension changed:", container.clientWidth, container.clientHeight);
});