JSFiddle - React, Tailwind, and code Playground

by Graham Fairweather

HTML

<div id="parent" class="parentDivStyle">
    <div class="childDivStyle">1</div>
    <div class="childDivStyle">2</div>
    <div class="childDivStyle">3</div>
    <div class="childDivStyle">4</div>
    <div class="childDivStyle">5</div>
</div>

CSS

.parentDivStyle {
    overflow:hidden;
    width:300px;
    height:50px;
    position:absolute;
    background:#ccc;
    float:left;
}
.childDivStyle {
    width:100px;
    height:50px;
    position:relative;
    float:left;
    background:red;
    border: 1px solid black;
}

JavaScript

function getNotVisible(parentId, childClassName) {
    var parent = document.getElementById(parentId),
        children,
        elements;

    if (parent) {
        children = parent.getElementsByClassName(childClassName);
        if (children) {
            elements = [];
            Array.prototype.forEach.call(children, function (child) {
                var pBounds = parent.getBoundingClientRect(),
                    cBounds = child.getBoundingClientRect();

                if (cBounds.right < pBounds.left || cBounds.left > pBounds.right || cBounds.bottom < pBounds.top || cBounds.top > pBounds.bottom) {
                    elements.push(child);
                }
            });
        }
    }

    return elements;
}

console.log(getNotVisible("parent", "childDivStyle"));