[javascript] How can I tell if a DOM element is visible in the current viewport?

Is there an efficient way to tell if a DOM element (in an HTML document) is currently visible (appears in the viewport)?

(The question refers to Firefox.)

I use this function (it only checks if the y is inscreen since most of the time the x is not needed)

function elementInViewport(el) {
    var elinfo = {
        "top":el.offsetTop,
        "height":el.offsetHeight,
    };

    if (elinfo.top + elinfo.height < window.pageYOffset || elinfo.top > window.pageYOffset + window.innerHeight) {
        return false;
    } else {
        return true;
    }

}

I find that the accepted answer here is overly complicated for most use cases. This code does the job well (using jQuery) and differentiates between fully visible and partially visible elements:

var element         = $("#element");
var topOfElement    = element.offset().top;
var bottomOfElement = element.offset().top + element.outerHeight(true);
var $window         = $(window);

$window.bind('scroll', function() {

    var scrollTopPosition   = $window.scrollTop()+$window.height();
    var windowScrollTop     = $window.scrollTop()

    if (windowScrollTop > topOfElement && windowScrollTop < bottomOfElement) {
        // Element is partially visible (above viewable area)
        console.log("Element is partially visible (above viewable area)");

    } else if (windowScrollTop > bottomOfElement && windowScrollTop > topOfElement) {
        // Element is hidden (above viewable area)
        console.log("Element is hidden (above viewable area)");

    } else if (scrollTopPosition < topOfElement && scrollTopPosition < bottomOfElement) {
        // Element is hidden (below viewable area)
        console.log("Element is hidden (below viewable area)");

    } else if (scrollTopPosition < bottomOfElement && scrollTopPosition > topOfElement) {
        // Element is partially visible (below viewable area)
        console.log("Element is partially visible (below viewable area)");

    } else {
        // Element is completely visible
        console.log("Element is completely visible");
    }
});

As simple as it can get, IMO:

function isVisible(elem) {
  var coords = elem.getBoundingClientRect();
  return Math.abs(coords.top) <= coords.height;
}

This checks if an element is at least partially in view (vertical dimension):

function inView(element) {
    var box = element.getBoundingClientRect();
    return inViewBox(box);
}

function inViewBox(box) {
    return ((box.bottom < 0) || (box.top > getWindowSize().h)) ? false : true;
}


function getWindowSize() {
    return { w: document.body.offsetWidth || document.documentElement.offsetWidth || window.innerWidth, h: document.body.offsetHeight || document.documentElement.offsetHeight || window.innerHeight}
}

The new Intersection Observer API addresses this question very directly.

This solution will need a polyfill as Safari, Opera and Internet Explorer don't support this yet (the polyfill is included in the solution).

In this solution, there is a box out of view that is the target (observed). When it comes into view, the button at the top in the header is hidden. It is shown once the box leaves the view.

const buttonToHide = document.querySelector('button');_x000D_
_x000D_
const hideWhenBoxInView = new IntersectionObserver((entries) => {_x000D_
  if (entries[0].intersectionRatio <= 0) { // If not in view_x000D_
    buttonToHide.style.display = "inherit";_x000D_
  } else {_x000D_
    buttonToHide.style.display = "none";_x000D_
  }_x000D_
});_x000D_
_x000D_
hideWhenBoxInView.observe(document.getElementById('box'));

header {_x000D_
  position: fixed;_x000D_
  top: 0;_x000D_
  width: 100vw;_x000D_
  height: 30px;_x000D_
  background-color: lightgreen;_x000D_
}_x000D_
_x000D_
.wrapper {_x000D_
  position: relative;_x000D_
  margin-top: 600px;_x000D_
}_x000D_
_x000D_
#box {_x000D_
  position: relative;_x000D_
  left: 175px;_x000D_
  width: 150px;_x000D_
  height: 135px;_x000D_
  background-color: lightblue;_x000D_
  border: 2px solid;_x000D_
}

<script src="https://polyfill.io/v2/polyfill.min.js?features=IntersectionObserver"></script>_x000D_
<header>_x000D_
  <button>NAVIGATION BUTTON TO HIDE</button>_x000D_
</header>_x000D_
  <div class="wrapper">_x000D_
    <div id="box">_x000D_
    </div>_x000D_
  </div>

All answers I've encountered here only check if the element is positioned inside the current viewport. But that doesn't mean that it is visible.
What if the given element is inside a div with overflowing content, and it is scrolled out of view?

To solve that, you'd have to check if the element is contained by all parents.
My solution does exactly that:

It also allows you to specify how much of the element has to be visible.

Element.prototype.isVisible = function(percentX, percentY){
    var tolerance = 0.01;   //needed because the rects returned by getBoundingClientRect provide the position up to 10 decimals
    if(percentX == null){
        percentX = 100;
    }
    if(percentY == null){
        percentY = 100;
    }

    var elementRect = this.getBoundingClientRect();
    var parentRects = [];
    var element = this;

    while(element.parentElement != null){
        parentRects.push(element.parentElement.getBoundingClientRect());
        element = element.parentElement;
    }

    var visibleInAllParents = parentRects.every(function(parentRect){
        var visiblePixelX = Math.min(elementRect.right, parentRect.right) - Math.max(elementRect.left, parentRect.left);
        var visiblePixelY = Math.min(elementRect.bottom, parentRect.bottom) - Math.max(elementRect.top, parentRect.top);
        var visiblePercentageX = visiblePixelX / elementRect.width * 100;
        var visiblePercentageY = visiblePixelY / elementRect.height * 100;
        return visiblePercentageX + tolerance > percentX && visiblePercentageY + tolerance > percentY;
    });
    return visibleInAllParents;
};

This solution ignored the fact that elements may not be visible due to other facts, like opacity: 0.

I have tested this solution in Chrome and Internet Explorer 11.

Most of the usages in previous answers are failing at these points:

-When any pixel of an element is visible, but not "a corner",

-When an element is bigger than viewport and centered,

-Most of them are checking only for a singular element inside a document or window.

Well, for all these problems I've a solution and the plus sides are:

-You can return visible when only a pixel from any sides shows up and is not a corner,

-You can still return visible while element bigger than viewport,

-You can choose your parent element or you can automatically let it choose,

-Works on dynamically added elements too.

If you check the snippets below you will see the difference in using overflow-scroll in element's container will not cause any trouble and see that unlike other answers here even if a pixel shows up from any side or when an element is bigger than viewport and we are seeing inner pixels of the element it still works.

Usage is simple:

// For checking element visibility from any sides
isVisible(element)

// For checking elements visibility in a parent you would like to check
var parent = document; // Assuming you check if 'element' inside 'document'
isVisible(element, parent)

// For checking elements visibility even if it's bigger than viewport
isVisible(element, null, true) // Without parent choice
isVisible(element, parent, true) // With parent choice

A demonstration without crossSearchAlgorithm which is usefull for elements bigger than viewport check element3 inner pixels to see:

function isVisible(element, parent, crossSearchAlgorithm) {_x000D_
    var rect = element.getBoundingClientRect(),_x000D_
            prect = (parent != undefined) ? parent.getBoundingClientRect() : element.parentNode.getBoundingClientRect(),_x000D_
        csa = (crossSearchAlgorithm != undefined) ? crossSearchAlgorithm : false,_x000D_
        efp = function (x, y) { return document.elementFromPoint(x, y) };_x000D_
    // Return false if it's not in the viewport_x000D_
    if (rect.right < prect.left || rect.bottom < prect.top || rect.left > prect.right || rect.top > prect.bottom) {_x000D_
        return false;_x000D_
    }_x000D_
    var flag = false;_x000D_
    // Return true if left to right any border pixel reached_x000D_
    for (var x = rect.left; x < rect.right; x++) {_x000D_
        if (element.contains(efp(rect.top, x)) || element.contains(efp(rect.bottom, x))) {_x000D_
        flag = true;_x000D_
        break;_x000D_
      }_x000D_
    }_x000D_
    // Return true if top to bottom any border pixel reached_x000D_
    if (flag == false) {_x000D_
      for (var y = rect.top; y < rect.bottom; y++) {_x000D_
        if (element.contains(efp(rect.left, y)) || element.contains(efp(rect.right, y))) {_x000D_
          flag = true;_x000D_
          break;_x000D_
        }_x000D_
      }_x000D_
    }_x000D_
    if(csa) {_x000D_
      // Another algorithm to check if element is centered and bigger than viewport_x000D_
      if (flag == false) {_x000D_
        var x = rect.left;_x000D_
        var y = rect.top;_x000D_
        // From top left to bottom right_x000D_
        while(x < rect.right || y < rect.bottom) {_x000D_
          if (element.contains(efp(x,y))) {_x000D_
            flag = true;_x000D_
            break;_x000D_
          }_x000D_
          if(x < rect.right) { x++; }_x000D_
          if(y < rect.bottom) { y++; }_x000D_
        }_x000D_
        if (flag == false) {_x000D_
          x = rect.right;_x000D_
          y = rect.top;_x000D_
          // From top right to bottom left_x000D_
          while(x > rect.left || y < rect.bottom) {_x000D_
            if (element.contains(efp(x,y))) {_x000D_
              flag = true;_x000D_
              break;_x000D_
            }_x000D_
            if(x > rect.left) { x--; }_x000D_
            if(y < rect.bottom) { y++; }_x000D_
          }_x000D_
        }_x000D_
      }_x000D_
    }_x000D_
    return flag;_x000D_
}_x000D_
_x000D_
// Check multiple elements visibility_x000D_
document.getElementById('container').addEventListener("scroll", function() {_x000D_
    var elementList = document.getElementsByClassName("element");_x000D_
  var console = document.getElementById('console');_x000D_
    for (var i=0; i < elementList.length; i++) {_x000D_
      // I did not define parent, so it will be element's parent_x000D_
    if (isVisible(elementList[i])) {_x000D_
          console.innerHTML = "Element with id[" + elementList[i].id + "] is visible!";_x000D_
      break;_x000D_
    } else {_x000D_
        console.innerHTML = "Element with id[" + elementList[i].id + "] is hidden!";_x000D_
    }_x000D_
  }_x000D_
});_x000D_
_x000D_
// Dynamically added elements_x000D_
for(var i=4; i <= 6; i++) {_x000D_
  var newElement = document.createElement("div");_x000D_
  newElement.id = "element" + i;_x000D_
  newElement.classList.add("element");_x000D_
  document.getElementById('container').appendChild(newElement);_x000D_
}

#console { background-color: yellow; }_x000D_
#container {_x000D_
  width: 300px;_x000D_
  height: 100px;_x000D_
  background-color: lightblue;_x000D_
  overflow-y: auto;_x000D_
  padding-top: 150px;_x000D_
  margin: 45px;_x000D_
}_x000D_
.element {_x000D_
  margin: 400px;_x000D_
  width: 400px;_x000D_
  height: 320px;_x000D_
  background-color: green;_x000D_
}_x000D_
#element3 {_x000D_
  position: relative;_x000D_
  margin: 40px;_x000D_
  width: 720px;_x000D_
  height: 520px;_x000D_
  background-color: green;_x000D_
}_x000D_
#element3::before {_x000D_
  content: "";_x000D_
  position: absolute;_x000D_
  top: -10px;_x000D_
  left: -10px;_x000D_
  margin: 0px;_x000D_
  width: 740px;_x000D_
  height: 540px;_x000D_
  border: 5px dotted green;_x000D_
  background: transparent;_x000D_
}

<div id="console"></div>_x000D_
<div id="container">_x000D_
    <div id="element1" class="element"></div>_x000D_
    <div id="element2" class="element"></div>_x000D_
    <div id="element3" class="element"></div>_x000D_
</div>

You see, when you are inside the element3 it fails to tell if it's visible or not, because we are only checking if the element is visible from sides or corners.

And this one includes crossSearchAlgorithm which allows you to still return visible when the element is bigger than the viewport:

function isVisible(element, parent, crossSearchAlgorithm) {_x000D_
    var rect = element.getBoundingClientRect(),_x000D_
            prect = (parent != undefined) ? parent.getBoundingClientRect() : element.parentNode.getBoundingClientRect(),_x000D_
        csa = (crossSearchAlgorithm != undefined) ? crossSearchAlgorithm : false,_x000D_
        efp = function (x, y) { return document.elementFromPoint(x, y) };_x000D_
    // Return false if it's not in the viewport_x000D_
    if (rect.right < prect.left || rect.bottom < prect.top || rect.left > prect.right || rect.top > prect.bottom) {_x000D_
        return false;_x000D_
    }_x000D_
    var flag = false;_x000D_
    // Return true if left to right any border pixel reached_x000D_
    for (var x = rect.left; x < rect.right; x++) {_x000D_
        if (element.contains(efp(rect.top, x)) || element.contains(efp(rect.bottom, x))) {_x000D_
        flag = true;_x000D_
        break;_x000D_
      }_x000D_
    }_x000D_
    // Return true if top to bottom any border pixel reached_x000D_
    if (flag == false) {_x000D_
      for (var y = rect.top; y < rect.bottom; y++) {_x000D_
        if (element.contains(efp(rect.left, y)) || element.contains(efp(rect.right, y))) {_x000D_
          flag = true;_x000D_
          break;_x000D_
        }_x000D_
      }_x000D_
    }_x000D_
    if(csa) {_x000D_
      // Another algorithm to check if element is centered and bigger than viewport_x000D_
      if (flag == false) {_x000D_
        var x = rect.left;_x000D_
        var y = rect.top;_x000D_
        // From top left to bottom right_x000D_
        while(x < rect.right || y < rect.bottom) {_x000D_
          if (element.contains(efp(x,y))) {_x000D_
            flag = true;_x000D_
            break;_x000D_
          }_x000D_
          if(x < rect.right) { x++; }_x000D_
          if(y < rect.bottom) { y++; }_x000D_
        }_x000D_
        if (flag == false) {_x000D_
          x = rect.right;_x000D_
          y = rect.top;_x000D_
          // From top right to bottom left_x000D_
          while(x > rect.left || y < rect.bottom) {_x000D_
            if (element.contains(efp(x,y))) {_x000D_
              flag = true;_x000D_
              break;_x000D_
            }_x000D_
            if(x > rect.left) { x--; }_x000D_
            if(y < rect.bottom) { y++; }_x000D_
          }_x000D_
        }_x000D_
      }_x000D_
    }_x000D_
    return flag;_x000D_
}_x000D_
_x000D_
// Check multiple elements visibility_x000D_
document.getElementById('container').addEventListener("scroll", function() {_x000D_
    var elementList = document.getElementsByClassName("element");_x000D_
  var console = document.getElementById('console');_x000D_
    for (var i=0; i < elementList.length; i++) {_x000D_
      // I did not define parent so it will be element's parent_x000D_
    // and it will do crossSearchAlgorithm_x000D_
    if (isVisible(elementList[i],null,true)) {_x000D_
          console.innerHTML = "Element with id[" + elementList[i].id + "] is visible!";_x000D_
      break;_x000D_
    } else {_x000D_
        console.innerHTML = "Element with id[" + elementList[i].id + "] is hidden!";_x000D_
    }_x000D_
  }_x000D_
});_x000D_
// Dynamically added elements_x000D_
for(var i=4; i <= 6; i++) {_x000D_
  var newElement = document.createElement("div");_x000D_
  newElement.id = "element" + i;_x000D_
  newElement.classList.add("element");_x000D_
  document.getElementById('container').appendChild(newElement);_x000D_
}

#console { background-color: yellow; }_x000D_
#container {_x000D_
  width: 300px;_x000D_
  height: 100px;_x000D_
  background-color: lightblue;_x000D_
  overflow-y: auto;_x000D_
  padding-top: 150px;_x000D_
  margin: 45px;_x000D_
}_x000D_
.element {_x000D_
  margin: 400px;_x000D_
  width: 400px;_x000D_
  height: 320px;_x000D_
  background-color: green;_x000D_
}_x000D_
#element3 {_x000D_
  position: relative;_x000D_
  margin: 40px;_x000D_
  width: 720px;_x000D_
  height: 520px;_x000D_
  background-color: green;_x000D_
}_x000D_
#element3::before {_x000D_
  content: "";_x000D_
  position: absolute;_x000D_
  top: -10px;_x000D_
  left: -10px;_x000D_
  margin: 0px;_x000D_
  width: 740px;_x000D_
  height: 540px;_x000D_
  border: 5px dotted green;_x000D_
  background: transparent;_x000D_
}

<div id="console"></div>_x000D_
<div id="container">_x000D_
    <div id="element1" class="element"></div>_x000D_
    <div id="element2" class="element"></div>_x000D_
    <div id="element3" class="element"></div>_x000D_
</div>

JSFiddle to play with: http://jsfiddle.net/BerkerYuceer/grk5az2c/

This code is made for more precise information if any part of the element is shown in the view or not. For performance options or only vertical slides, do not use this! This code is more effective in drawing cases.

As a public service:
Dan's answer with the correct calculations (element can be > window, especially on mobile phone screens), and correct jQuery testing, as well as adding isElementPartiallyInViewport:

By the way, the difference between window.innerWidth and document.documentElement.clientWidth is that clientWidth/clientHeight doesn't include the scrollbar, while window.innerWidth/Height does.

function isElementPartiallyInViewport(el)
{
    // Special bonus for those using jQuery
    if (typeof jQuery !== 'undefined' && el instanceof jQuery) 
        el = el[0];

    var rect = el.getBoundingClientRect();
    // DOMRect { x: 8, y: 8, width: 100, height: 100, top: 8, right: 108, bottom: 108, left: 8 }
    var windowHeight = (window.innerHeight || document.documentElement.clientHeight);
    var windowWidth = (window.innerWidth || document.documentElement.clientWidth);

    // http://stackoverflow.com/questions/325933/determine-whether-two-date-ranges-overlap
    var vertInView = (rect.top <= windowHeight) && ((rect.top + rect.height) >= 0);
    var horInView = (rect.left <= windowWidth) && ((rect.left + rect.width) >= 0);

    return (vertInView && horInView);
}


// http://stackoverflow.com/questions/123999/how-to-tell-if-a-dom-element-is-visible-in-the-current-viewport
function isElementInViewport (el)
{
    // Special bonus for those using jQuery
    if (typeof jQuery !== 'undefined' && el instanceof jQuery) 
        el = el[0];

    var rect = el.getBoundingClientRect();
    var windowHeight = (window.innerHeight || document.documentElement.clientHeight);
    var windowWidth = (window.innerWidth || document.documentElement.clientWidth);

    return (
           (rect.left >= 0)
        && (rect.top >= 0)
        && ((rect.left + rect.width) <= windowWidth)
        && ((rect.top + rect.height) <= windowHeight)
    );
}


function fnIsVis(ele)
{
    var inVpFull = isElementInViewport(ele);
    var inVpPartial = isElementPartiallyInViewport(ele);
    console.clear();
    console.log("Fully in viewport: " + inVpFull);
    console.log("Partially in viewport: " + inVpPartial);
}

Test-case

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <meta name="description" content="">
    <meta name="author" content="">
    <title>Test</title>
    <!--
    <script src="http://cdnjs.cloudflare.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
    <script src="scrollMonitor.js"></script>
    -->

    <script type="text/javascript">

        function isElementPartiallyInViewport(el)
        {
            // Special bonus for those using jQuery
            if (typeof jQuery !== 'undefined' && el instanceof jQuery) 
                el = el[0];

            var rect = el.getBoundingClientRect();
            // DOMRect { x: 8, y: 8, width: 100, height: 100, top: 8, right: 108, bottom: 108, left: 8 }
            var windowHeight = (window.innerHeight || document.documentElement.clientHeight);
            var windowWidth = (window.innerWidth || document.documentElement.clientWidth);

            // http://stackoverflow.com/questions/325933/determine-whether-two-date-ranges-overlap
            var vertInView = (rect.top <= windowHeight) && ((rect.top + rect.height) >= 0);
            var horInView = (rect.left <= windowWidth) && ((rect.left + rect.width) >= 0);

            return (vertInView && horInView);
        }


        // http://stackoverflow.com/questions/123999/how-to-tell-if-a-dom-element-is-visible-in-the-current-viewport
        function isElementInViewport (el)
        {
            // Special bonus for those using jQuery
            if (typeof jQuery !== 'undefined' && el instanceof jQuery) 
                el = el[0];

            var rect = el.getBoundingClientRect();
            var windowHeight = (window.innerHeight || document.documentElement.clientHeight);
            var windowWidth = (window.innerWidth || document.documentElement.clientWidth);

            return (
                   (rect.left >= 0)
                && (rect.top >= 0)
                && ((rect.left + rect.width) <= windowWidth)
                && ((rect.top + rect.height) <= windowHeight)
            );
        }


        function fnIsVis(ele)
        {
            var inVpFull = isElementInViewport(ele);
            var inVpPartial = isElementPartiallyInViewport(ele);
            console.clear();
            console.log("Fully in viewport: " + inVpFull);
            console.log("Partially in viewport: " + inVpPartial);
        }


        // var scrollLeft = (window.pageXOffset !== undefined) ? window.pageXOffset : (document.documentElement || document.body.parentNode || document.body).scrollLeft,
        // var scrollTop = (window.pageYOffset !== undefined) ? window.pageYOffset : (document.documentElement || document.body.parentNode || document.body).scrollTop;
    </script>
</head>

<body>
    <div style="display: block; width: 2000px; height: 10000px; background-color: green;">

        <br /><br /><br /><br /><br /><br />
        <br /><br /><br /><br /><br /><br />
        <br /><br /><br /><br /><br /><br />

        <input type="button" onclick="fnIsVis(document.getElementById('myele'));" value="det" />

        <br /><br /><br /><br /><br /><br />
        <br /><br /><br /><br /><br /><br />
        <br /><br /><br /><br /><br /><br />

        <div style="background-color: crimson; display: inline-block; width: 800px; height: 500px;" ></div>
        <div id="myele" onclick="fnIsVis(this);" style="display: inline-block; width: 100px; height: 100px; background-color: hotpink;">
        t
        </div>

        <br /><br /><br /><br /><br /><br />
        <br /><br /><br /><br /><br /><br />
        <br /><br /><br /><br /><br /><br />

        <input type="button" onclick="fnIsVis(document.getElementById('myele'));" value="det" />
    </div>

    <!--
    <script type="text/javascript">

        var element = document.getElementById("myele");
        var watcher = scrollMonitor.create(element);

        watcher.lock();

        watcher.stateChange(function() {
            console.log("state changed");
            // $(element).toggleClass('fixed', this.isAboveViewport)
        });
    </script>
    -->
</body>
</html>

I found it troubling that there wasn't a jQuery-centric version of the functionality available. When I came across Dan's solution I spied the opportunity to provide something for folks who like to program in the jQuery OO style. It's nice and snappy and works like a charm for me.

Bada bing bada boom

$.fn.inView = function(){
    if(!this.length) 
        return false;
    var rect = this.get(0).getBoundingClientRect();

    return (
        rect.top >= 0 &&
        rect.left >= 0 &&
        rect.bottom <= (window.innerHeight || document.documentElement.clientHeight) &&
        rect.right <= (window.innerWidth || document.documentElement.clientWidth)
    );

};

// Additional examples for other use cases
// Is true false whether an array of elements are all in view
$.fn.allInView = function(){
    var all = [];
    this.forEach(function(){
        all.push( $(this).inView() );
    });
    return all.indexOf(false) === -1;
};

// Only the class elements in view
$('.some-class').filter(function(){
    return $(this).inView();
});

// Only the class elements not in view
$('.some-class').filter(function(){
    return !$(this).inView();
});

Usage

$(window).on('scroll',function(){

    if( $('footer').inView() ) {
        // Do cool stuff
    }
});

Now most browsers support getBoundingClientRect method, which has become the best practice. Using an old answer is very slow, not accurate and has several bugs.

The solution selected as correct is almost never precise. You can read more about its bugs.

This solution was tested on Internet Explorer 7 (and later), iOS 5 (and later) Safari, Android 2.0 (Eclair) and later, BlackBerry, Opera Mobile, and Internet Explorer Mobile ⁹.

function isElementInViewport (el) {

    // Special bonus for those using jQuery
    if (typeof jQuery === "function" && el instanceof jQuery) {
        el = el[0];
    }

    var rect = el.getBoundingClientRect();

    return (
        rect.top >= 0 &&
        rect.left >= 0 &&
        rect.bottom <= (window.innerHeight || document.documentElement.clientHeight) && /* or $(window).height() */
        rect.right <= (window.innerWidth || document.documentElement.clientWidth) /* or $(window).width() */
    );
}

How to use:

You can be sure that the function given above returns correct answer at the moment of time when it is called, but what about tracking element's visibility as an event?

Place the following code at the bottom of your <body> tag:

function onVisibilityChange(el, callback) {
    var old_visible;
    return function () {
        var visible = isElementInViewport(el);
        if (visible != old_visible) {
            old_visible = visible;
            if (typeof callback == 'function') {
                callback();
            }
        }
    }
}

var handler = onVisibilityChange(el, function() {
    /* Your code go here */
});


// jQuery
$(window).on('DOMContentLoaded load resize scroll', handler);

/* // Non-jQuery
if (window.addEventListener) {
    addEventListener('DOMContentLoaded', handler, false);
    addEventListener('load', handler, false);
    addEventListener('scroll', handler, false);
    addEventListener('resize', handler, false);
} else if (window.attachEvent)  {
    attachEvent('onDOMContentLoaded', handler); // Internet Explorer 9+ :(
    attachEvent('onload', handler);
    attachEvent('onscroll', handler);
    attachEvent('onresize', handler);
}
*/

If you do any DOM modifications, they can change your element's visibility of course.

Guidelines and common pitfalls:

Maybe you need to track page zoom / mobile device pinch? jQuery should handle zoom/pinch cross browser, otherwise first or second link should help you.

If you modify DOM, it can affect the element's visibility. You should take control over that and call handler() manually. Unfortunately, we don't have any cross browser onrepaint event. On the other hand that allows us to make optimizations and perform re-check only on DOM modifications that can change an element's visibility.

Never Ever use it inside jQuery $(document).ready() only, because there is no warranty CSS has been applied in this moment. Your code can work locally with your CSS on a hard drive, but once put on a remote server it will fail.

After DOMContentLoaded is fired, styles are applied, but the images are not loaded yet. So, we should add window.onload event listener.

We can't catch zoom/pinch event yet.

The last resort could be the following code:

/* TODO: this looks like a very bad code */
setInterval(handler, 600);

You can use the awesome feature pageVisibiliy of the HTML5 API if you care if the tab with your web page is active and visible.

TODO: this method does not handle two situations:

• overlapping using z-index
• using overflow-scroll in element's container
• try something new - The Intersection Observer API explained

I had the same question and figured it out by using getBoundingClientRect().

This code is completely 'generic' and only has to be written once for it to work (you don't have to write it out for each element that you want to know is in the viewport).

This code only checks to see if it is vertically in the viewport, not horizontally. In this case, the variable (array) 'elements' holds all the elements that you are checking to be vertically in the viewport, so grab any elements you want anywhere and store them there.

The 'for loop', loops through each element and checks to see if it is vertically in the viewport. This code executes every time the user scrolls! If the getBoudingClientRect().top is less than 3/4 the viewport (the element is one quarter in the viewport), it registers as 'in the viewport'.

Since the code is generic, you will want to know 'which' element is in the viewport. To find that out, you can determine it by custom attribute, node name, id, class name, and more.

Here is my code (tell me if it doesn't work; it has been tested in Internet Explorer 11, Firefox 40.0.3, Chrome Version 45.0.2454.85 m, Opera 31.0.1889.174, and Edge with Windows 10, [not Safari yet])...

// Scrolling handlers...
window.onscroll = function(){
  var elements = document.getElementById('whatever').getElementsByClassName('whatever');
  for(var i = 0; i != elements.length; i++)
  {
   if(elements[i].getBoundingClientRect().top <= window.innerHeight*0.75 &&
      elements[i].getBoundingClientRect().top > 0)
   {
      console.log(elements[i].nodeName + ' ' +
                  elements[i].className + ' ' +
                  elements[i].id +
                  ' is in the viewport; proceed with whatever code you want to do here.');
   }
};

I think this is a more functional way to do it. Dan's answer do not work in a recursive context.

This function solves the problem when your element is inside others scrollable divs by testing any levels recursively up to the HTML tag, and stops at the first false.

/**
 * fullVisible=true only returns true if the all object rect is visible
 */
function isReallyVisible(el, fullVisible) {
    if ( el.tagName == "HTML" )
            return true;
    var parentRect=el.parentNode.getBoundingClientRect();
    var rect = arguments[2] || el.getBoundingClientRect();
    return (
            ( fullVisible ? rect.top    >= parentRect.top    : rect.bottom > parentRect.top ) &&
            ( fullVisible ? rect.left   >= parentRect.left   : rect.right  > parentRect.left ) &&
            ( fullVisible ? rect.bottom <= parentRect.bottom : rect.top    < parentRect.bottom ) &&
            ( fullVisible ? rect.right  <= parentRect.right  : rect.left   < parentRect.right ) &&
            isReallyVisible(el.parentNode, fullVisible, rect)
    );
};

The most accepted answers don't work when zooming in Google Chrome on Android. In combination with Dan's answer, to account for Chrome on Android, visualViewport must be used. The following example only takes the vertical check into account and uses jQuery for the window height:

var Rect = YOUR_ELEMENT.getBoundingClientRect();
var ElTop = Rect.top, ElBottom = Rect.bottom;
var WindowHeight = $(window).height();
if(window.visualViewport) {
    ElTop -= window.visualViewport.offsetTop;
    ElBottom -= window.visualViewport.offsetTop;
    WindowHeight = window.visualViewport.height;
}
var WithinScreen = (ElTop >= 0 && ElBottom <= WindowHeight);

Update

In modern browsers, you might want to check out the Intersection Observer API which provides the following benefits:

• Better performance than listening for scroll events
• Works in cross domain iframes
• Can tell if an element is obstructing/intersecting another

Intersection Observer is on its way to being a full-fledged standard and is already supported in Chrome 51+, Edge 15+ and Firefox 55+ and is under development for Safari. There's also a polyfill available.

Previous answer

There are some issues with the answer provided by Dan that might make it an unsuitable approach for some situations. Some of these issues are pointed out in his answer near the bottom, that his code will give false positives for elements that are:

• Hidden by another element in front of the one being tested
• Outside the visible area of a parent or ancestor element
• An element or its children hidden by using the CSS clip property

These limitations are demonstrated in the following results of a simple test:

The solution: isElementVisible()

Here's a solution to those problems, with the test result below and an explanation of some parts of the code.

function isElementVisible(el) {
    var rect     = el.getBoundingClientRect(),
        vWidth   = window.innerWidth || document.documentElement.clientWidth,
        vHeight  = window.innerHeight || document.documentElement.clientHeight,
        efp      = function (x, y) { return document.elementFromPoint(x, y) };     

    // Return false if it's not in the viewport
    if (rect.right < 0 || rect.bottom < 0 
            || rect.left > vWidth || rect.top > vHeight)
        return false;

    // Return true if any of its four corners are visible
    return (
          el.contains(efp(rect.left,  rect.top))
      ||  el.contains(efp(rect.right, rect.top))
      ||  el.contains(efp(rect.right, rect.bottom))
      ||  el.contains(efp(rect.left,  rect.bottom))
    );
}

Passing test: http://jsfiddle.net/AndyE/cAY8c/

And the result:

Additional notes

This method is not without its own limitations, however. For instance, an element being tested with a lower z-index than another element at the same location would be identified as hidden even if the element in front doesn't actually hide any part of it. Still, this method has its uses in some cases that Dan's solution doesn't cover.

Both element.getBoundingClientRect() and document.elementFromPoint() are part of the CSSOM Working Draft specification and are supported in at least IE 6 and later and most desktop browsers for a long time (albeit, not perfectly). See Quirksmode on these functions for more information.

contains() is used to see if the element returned by document.elementFromPoint() is a child node of the element we're testing for visibility. It also returns true if the element returned is the same element. This just makes the check more robust. It's supported in all major browsers, Firefox 9.0 being the last of them to add it. For older Firefox support, check this answer's history.

If you want to test more points around the element for visibility-ie, to make sure the element isn't covered by more than, say, 50%-it wouldn't take much to adjust the last part of the answer. However, be aware that it would probably be very slow if you checked every pixel to make sure it was 100% visible.

This is the easy and small solution that has worked for me.

Example: You want to see if the element is visible in the parent element that has overflow scroll.

$(window).on('scroll', function () {

     var container = $('#sidebar');
     var containerHeight = container.height();
     var scrollPosition = $('#row1').offset().top - container.offset().top;

     if (containerHeight < scrollPosition) {
         console.log('not visible');
     } else {
         console.log('visible');
     }
})

Based on dan's solution, I had a go at cleaning up the implementation so that using it multiple times on the same page is easier:

$(function() {

  $(window).on('load resize scroll', function() {
    addClassToElementInViewport($('.bug-icon'), 'animate-bug-icon');
    addClassToElementInViewport($('.another-thing'), 'animate-thing');
    //  repeat as needed ...
  });

  function addClassToElementInViewport(element, newClass) {
    if (inViewport(element)) {
      element.addClass(newClass);
    }
  }

  function inViewport(element) {
    if (typeof jQuery === "function" && element instanceof jQuery) {
      element = element[0];
    }
    var elementBounds = element.getBoundingClientRect();
    return (
      elementBounds.top >= 0 &&
      elementBounds.left >= 0 &&
      elementBounds.bottom <= $(window).height() &&
      elementBounds.right <= $(window).width()
    );
  }

});

The way I'm using it is that when the element scrolls into view, I'm adding a class that triggers a CSS keyframe animation. It's pretty straightforward and works especially well when you've got like 10+ things to conditionally animate on a page.

A better solution:

function getViewportSize(w) {
    var w = w || window;
    if(w.innerWidth != null)
        return {w:w.innerWidth, h:w.innerHeight};
    var d = w.document;
    if (document.compatMode == "CSS1Compat") {
        return {
            w: d.documentElement.clientWidth,
            h: d.documentElement.clientHeight
        };
    }
    return { w: d.body.clientWidth, h: d.body.clientWidth };
}


function isViewportVisible(e) {
    var box = e.getBoundingClientRect();
    var height = box.height || (box.bottom - box.top);
    var width = box.width || (box.right - box.left);
    var viewport = getViewportSize();
    if(!height || !width)
        return false;
    if(box.top > viewport.h || box.bottom < 0)
        return false;
    if(box.right < 0 || box.left > viewport.w)
        return false;
    return true;
}

All the answers here are determining if the element is fully contained within the viewport, not just visible in some way. For example, if only half of an image is visible at the bottom of the view, the solutions here will fail, considering that "outside".

I had a use case where I'm doing lazy loading via IntersectionObserver, but due to animations that occur during pop-in, I didn't want to observe any images that were already intersected on page load. To do that, I used the following code:

const bounding = el.getBoundingClientRect();
const isVisible = (0 < bounding.top && bounding.top < (window.innerHeight || document.documentElement.clientHeight)) ||
        (0 < bounding.bottom && bounding.bottom < (window.innerHeight || document.documentElement.clientHeight));

This is basically checking to see if either the top or bottom bound is independently in the viewport. The opposite end may be outside, but as long as one end is in, it's "visible" at least partially.

See the source of verge, which uses getBoundingClientRect. It's like:

function inViewport (el) {

    var r, html;
    if ( !el || 1 !== el.nodeType ) { return false; }
    html = document.documentElement;
    r = el.getBoundingClientRect();

    return ( !!r
      && r.bottom >= 0
      && r.right >= 0
      && r.top <= html.clientHeight
      && r.left <= html.clientWidth
    );

}

It returns true if any part of the element is in the viewport.

My shorter and faster version:

function isElementOutViewport(el){
    var rect = el.getBoundingClientRect();
    return rect.bottom < 0 || rect.right < 0 || rect.left > window.innerWidth || rect.top > window.innerHeight;
}

And a jsFiddle as required: https://jsfiddle.net/on1g619L/1/

For a similar challenge, I really enjoyed this gist which exposes a polyfill for scrollIntoViewIfNeeded().

All the necessary Kung Fu needed to answer is within this block:

var parent = this.parentNode,
    parentComputedStyle = window.getComputedStyle(parent, null),
    parentBorderTopWidth = parseInt(parentComputedStyle.getPropertyValue('border-top-width')),
    parentBorderLeftWidth = parseInt(parentComputedStyle.getPropertyValue('border-left-width')),
    overTop = this.offsetTop - parent.offsetTop < parent.scrollTop,
    overBottom = (this.offsetTop - parent.offsetTop + this.clientHeight - parentBorderTopWidth) > (parent.scrollTop + parent.clientHeight),
    overLeft = this.offsetLeft - parent.offsetLeft < parent.scrollLeft,
    overRight = (this.offsetLeft - parent.offsetLeft + this.clientWidth - parentBorderLeftWidth) > (parent.scrollLeft + parent.clientWidth),
    alignWithTop = overTop && !overBottom;

this refers to the element that you want to know if it is, for example, overTop or overBottom - you just should get the drift...

Here's my solution. It will work if an element is hidden inside a scrollable container.

Here's a demo (try re-sizing the window to)

var visibleY = function(el){
    var top = el.getBoundingClientRect().top, rect, el = el.parentNode;
    do {
        rect = el.getBoundingClientRect();
        if (top <= rect.bottom === false)
            return false;
        el = el.parentNode;
    } while (el != document.body);
    // Check it's within the document viewport
    return top <= document.documentElement.clientHeight;
};

I only needed to check if it's visible in the Y axis (for a scrolling Ajax load-more-records feature).

The simplest solution as the support of Element.getBoundingClientRect() has become perfect:

function isInView(el) {
  let box = el.getBoundingClientRect();
  return box.top < window.innerHeight && box.bottom >= 0;
}

I tried Dan's answer. However, the algebra used to determine the bounds means that the element must be both = the viewport size and completely inside the viewport to get true, easily leading to false negatives. If you want to determine whether an element is in the viewport at all, ryanve's answer is close, but the element being tested should overlap the viewport, so try this:

function isElementInViewport(el) {
    var rect = el.getBoundingClientRect();

    return rect.bottom > 0 &&
        rect.right > 0 &&
        rect.left < (window.innerWidth || document.documentElement.clientWidth) /* or $(window).width() */ &&
        rect.top < (window.innerHeight || document.documentElement.clientHeight) /* or $(window).height() */;
}

Here is a function that tells if an element is in visible in the current viewport of a parent element:

function inParentViewport(el, pa) {
    if (typeof jQuery === "function"){
        if (el instanceof jQuery)
            el = el[0];
        if (pa instanceof jQuery)
            pa = pa[0];
    }

    var e = el.getBoundingClientRect();
    var p = pa.getBoundingClientRect();

    return (
        e.bottom >= p.top &&
        e.right >= p.left &&
        e.top <= p.bottom &&
        e.left <= p.right
    );
}