Detect when elements within a scrollable div are out of view

Question

I need to find a good solution to the following problem. I see a lot of people asking about tracking if an element is in or outside of view Port for the page or browser window. I need to be able to replicate this action, but inside a DIV that scrolls, with overflow:scroll for example. Does anyone know of a good example, for this specific action?

Thanks in advance.

Answer 1

Here's a pure javascript version of the accepted answer without relying on jQuery and with some fixes to the partial in view detection and support for out of view on top.

function checkInView(container, element, partial) {

    //Get container properties
    let cTop = container.scrollTop;
    let cBottom = cTop + container.clientHeight;

    //Get element properties
    let eTop = element.offsetTop;
    let eBottom = eTop + element.clientHeight;

    //Check if in view    
    let isTotal = (eTop >= cTop && eBottom <= cBottom);
    let isPartial = partial && (
      (eTop < cTop && eBottom > cTop) ||
      (eBottom > cBottom && eTop < cBottom)
    );

    //Return outcome
    return  (isTotal  || isPartial);
}

And as a bonus, this function ensures the element is in view if it's not (partial or full):

function ensureInView(container, element) {

    //Determine container top and bottom
    let cTop = container.scrollTop;
    let cBottom = cTop + container.clientHeight;

    //Determine element top and bottom
    let eTop = element.offsetTop;
    let eBottom = eTop + element.clientHeight;

    //Check if out of view
    if (eTop < cTop) {
      container.scrollTop -= (cTop - eTop);
    }
    else if (eBottom > cBottom) {
      container.scrollTop += (eBottom - cBottom);
    }
}

Answer 2

i had the same problem before, i have ended up with the following function.the first parameter is for the element to check, the second is to check if the element is partially in-view.it is for vertical check only, you can extend it to check for horizontal scroll.

function checkInView(elem,partial)
{
    var container = $(".scrollable");
    var contHeight = container.height();
    var contTop = container.scrollTop();
    var contBottom = contTop + contHeight ;

    var elemTop = $(elem).offset().top - container.offset().top;
    var elemBottom = elemTop + $(elem).height();

    var isTotal = (elemTop >= 0 && elemBottom <=contHeight);
    var isPart = ((elemTop < 0 && elemBottom > 0 ) || (elemTop > 0 && elemTop <= container.height())) && partial ;

    return  isTotal  || isPart ;
}

check it on jsFiddle .

Answer 3

Based of the best answer. Instead of just telling you if an element is partially visible or not. I added a little extra so you can pass in a percentage (0-100) that tells you if the element is more than x% visible.

function (container, element, partial) {
    var cTop = container.scrollTop;
    var cBottom = cTop + container.clientHeight;
    var eTop = element.offsetTop;
    var eBottom = eTop + element.clientHeight;
    var isTotal = (eTop >= cTop && eBottom <= cBottom);
    var isPartial;

    if (partial === true) {
        isPartial = (eTop < cTop && eBottom > cTop) || (eBottom > cBottom && eTop < cBottom);
    } else if(typeof partial === "number"){
        if (eTop < cTop && eBottom > cTop) {
            isPartial = ((eBottom - cTop) * 100) / element.clientHeight > partial;
        } else if (eBottom > cBottom && eTop < cBottom){ 
            isPartial = ((cBottom - eTop) * 100) / element.clientHeight > partial;
        }
    }
    return (isTotal || isPartial);
}