CODEWITHSUNDEEP
javascriptjqueryscrollviewportoffset
youyoup
youyoup

Reputation: 619

JS - get percentage of an element in Viewport

I want to get the percentage of an element (div) when its in viewport.

Here are 5 viewports of what I want to do https://i.sstatic.net/qaH97.jpg

I tried : 

$(window).bind('scroll',function(){
var  viewportHeight = $(window).height(),
elementOffsetTop = $('#element').offset().top,
elementHeight = $('#element').height();

var numerator = 200 * (window.pageYOffset-elementOffsetTop+viewportHeight);
var denominator = (elementOffset+elementHeight+viewportHeight);
console.log(numerator/denominator);
});

This code works. (I don't understand why I have to multiply by 2).

But when I resize my page, this code not works ( value between 0 to 85 ... )

Ideas?

Upvotes: 15

Views: 13272

Answers (2)

Nate
Nate

Reputation: 4948

UPDATE: It seems like this still gets a little bit of traffic, so here's an updated solution that doesn't use jQuery.

http://jsfiddle.net/nate/nmvka95j/20/

const element = document.getElementById("element");
const visible = document.getElementById("visible");

const logPercentageSeen = () => {
  console.log(percentageSeen());
  visible.textContent = `${percentageSeen()} %`;
};

window.addEventListener("scroll", logPercentageSeen);

const percentageSeen = () => {
  // Get the relevant measurements and positions
  const viewportHeight = window.innerHeight;
  const scrollTop = window.scrollY;
  const elementOffsetTop = element.offsetTop;
  const elementHeight = element.offsetHeight;

  // Calculate percentage of the element that's been seen
  const distance = scrollTop + viewportHeight - elementOffsetTop;
  const percentage = Math.round(
    distance / ((viewportHeight + elementHeight) / 100)
  );

  // Restrict the range to between 0 and 100
  return Math.min(100, Math.max(0, percentage));
};

// Log the initial value to the top before any scrolling has happened
logPercentageSeen();

Here's the old solution, pre-ES6 and using our old, dear friend jQuery.

http://jsfiddle.net/nate/4N3Pj/1/

var $element = $('#element');
var $win = $(window);
var $vis = $('#visible');

$win.on('scroll', function () {
    console.log(percentageSeen());
    $vis.text(percentageSeen() + '%');
});

function percentageSeen () {
    var viewportHeight = $(window).height(),
        scrollTop = $win.scrollTop(),
        elementOffsetTop = $element.offset().top,
        elementHeight = $element.height();


    if (elementOffsetTop > (scrollTop + viewportHeight)) {
        return 0;
    } else if ((elementOffsetTop + elementHeight) < scrollTop) {
        return 100;
    } else {
        var distance = (scrollTop + viewportHeight) - elementOffsetTop;
        var percentage = distance / ((viewportHeight + elementHeight) / 100);
        percentage = Math.round(percentage);
        return percentage;
    }
}

$win.trigger('scroll');

Upvotes: 20

Floris
Floris

Reputation: 3127

My version is slightly different. When the element is higher than the screen height itself, it interprets that as 100% in viewport.

For example, if the screen height is 1000 pixels and the element is 2000 pixels height and it is scrolled fully into view, the function will return 100% instead of the normal 50%.

Enjoy.

var percentWithinViewport = function (element) {

    var elementTop = element.offset().top;
    var scrollTop = $(window).scrollTop();
    var spaceTop = elementTop - scrollTop;
    var elementHeight = element.height();
    var screenHeight = $(window).height();
    var scrollBottom = scrollTop + screenHeight;
    var bottomElement = elementTop + element.height();
    var spaceBottom = bottomElement - scrollBottom;
    var heightInScreen = elementHeight - spaceBottom;
    var percentage;

    if (spaceTop < 0) {
        heightInScreen -= spaceTop * -1;
    }

    if (spaceBottom < 0) {
        heightInScreen -= spaceBottom * -1;
    }

    percentage = heightInScreen / screenHeight * 100;
    percentage = percentage < 0 ? 0 : percentage;

    element.attr('data-percent-viewport', percentage);

    return percentage;
};

Upvotes: 5

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