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

由 生来就可爱ヽ(ⅴ＜●) 提交于 2019-12-23 15:31:57

问题


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.)


回答1:


Update: Time marches on and so have our browsers. This technique is no longer recommended and you should use @Dan's solution below (https://stackoverflow.com/a/7557433/5628) if you do not need to support IE<7.

Original solution (now outdated):

This will check if the element is entirely visible in the current viewport:

function elementInViewport(el) {
  var top = el.offsetTop;
  var left = el.offsetLeft;
  var width = el.offsetWidth;
  var height = el.offsetHeight;

  while(el.offsetParent) {
    el = el.offsetParent;
    top += el.offsetTop;
    left += el.offsetLeft;
  }

  return (
    top >= window.pageYOffset &&
    left >= window.pageXOffset &&
    (top + height) <= (window.pageYOffset + window.innerHeight) &&
    (left + width) <= (window.pageXOffset + window.innerWidth)
  );
}

You could modify this simply to determine if any part of the element is visible in the viewport:

function elementInViewport2(el) {
  var top = el.offsetTop;
  var left = el.offsetLeft;
  var width = el.offsetWidth;
  var height = el.offsetHeight;

  while(el.offsetParent) {
    el = el.offsetParent;
    top += el.offsetTop;
    left += el.offsetLeft;
  }

  return (
    top < (window.pageYOffset + window.innerHeight) &&
    left < (window.pageXOffset + window.innerWidth) &&
    (top + height) > window.pageYOffset &&
    (left + width) > window.pageXOffset
  );
}



回答2:


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 IE7+, iOS5+ Safari, Android2+, Blackberry, Opera Mobile, and IE Mobile 10.

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); // IE9+ :(
    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 have no 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 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 hard drive, but once put on 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 awesome feature pageVisibiliy 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 https://pawelgrzybek.com/the-intersection-observer-api-explained/




回答3:


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 || doc.documentElement.clientWidth,
        vHeight  = window.innerHeight || doc.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.




回答4:


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() */;
}



回答5:


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>



回答6:


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 
    );

}

Returns true if any part of the element is in the viewport.




回答7:


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;
}

add jsFiddle as required https://jsfiddle.net/on1g619L/1/




回答8:


There is jQuery plugin called inview that does the job




回答9:


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. Be sure to scroll up and leave an upvote on Dan's code. Its 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
//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
    }

});



回答10:


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");
    }
});



回答11:


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.




回答12:


The new Intersection Observer API addresses this question very directly.

This solution will need a polyfill as Safari, Opera and IE 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');

const hideWhenBoxInView = new IntersectionObserver((entries) => {
  if (entries[0].intersectionRatio <= 0) { // If not in view
    buttonToHide.style.display = "inherit";
  } else {
    buttonToHide.style.display = "none";
  }
});

hideWhenBoxInView.observe(document.getElementById('box'));
header {
  position: fixed;
  top: 0;
  width: 100vw;
  height: 30px;
  background-color: lightgreen;
}

.wrapper {
  position: relative;
  margin-top: 600px;
}

#box {
  position: relative;
  left: 175px;
  width: 150px;
  height: 135px;
  background-color: lightblue;
  border: 2px solid;
}
<script src="https://polyfill.io/v2/polyfill.min.js?features=IntersectionObserver"></script>
<header>
  <button>NAVIGATION BUTTON TO HIDE</button>
</header>
  <div class="wrapper">
    <div id="box">
    </div>
  </div>



回答13:


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

This function solve the problem when your element is inside others scrollable divs by testing any levels recursively upper to the HTML tag, and stops in 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)
    );
};



回答14:


Here's my solution, it will work if an element is hidden inside a scroll-able 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 its 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).




回答15:


Based on @dan's solution above (https://stackoverflow.com/a/7557433/5628), I had a go at cleaning up 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.

Hope it helps!




回答16:


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;    
}



回答17:


The easy and small solution that has worked for me.

Example You want to see if the element is visible in 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');
     }
})



回答18:


Attention everyone!

Most of the usages up here failing at these points:

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

-When element is bigger than viewport and centered,

-Most of them are checking only for a singular element inside 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 element is bigger then 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; // Asuming you check if element inside document
isVisible(element, parent)

// For checking elements visibility even if its bigger then viewport
isVisible(element, null, true) // Without parent choise
isVisible(element, parent, true) // With parent choise

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

function isVisible(element, parent, crossSearchAlgorithm) {
    var rect = element.getBoundingClientRect(),
    		prect = (parent != undefined) ? parent.getBoundingClientRect() : element.parentNode.getBoundingClientRect(),
        csa = (crossSearchAlgorithm != undefined) ? crossSearchAlgorithm : false,
        efp = function (x, y) { return document.elementFromPoint(x, y) };
    // Return false if it's not in the viewport
    if (rect.right < prect.left || rect.bottom < prect.top || rect.left > prect.right || rect.top > prect.bottom) {
        return false;
    }
    var flag = false;
    // Return true if left to right any border pixel reached 
    for (var x = rect.left; x < rect.right; x++) {
    	if (element.contains(efp(rect.top, x)) || element.contains(efp(rect.bottom, x))) {
        flag = true;
        break;
      }
    }
    // Return true if top to bottom any border pixel reached 
    if (flag == false) {
      for (var y = rect.top; y < rect.bottom; y++) {
        if (element.contains(efp(rect.left, y)) || element.contains(efp(rect.right, y))) {
          flag = true;
          break;
        }
      }
    }
    if(csa) {
      // Another algorithm to check if element is centered and bigger than viewport
      if (flag == false) {
        var x = rect.left;
        var y = rect.top;
        // From top left to bottom right
        while(x < rect.right || y < rect.bottom) {
          if (element.contains(efp(x,y))) {
            flag = true;
            break;
          }
          if(x < rect.right) { x++; }
          if(y < rect.bottom) { y++; }
        }
        if (flag == false) {
          x = rect.right;
          y = rect.top;
          // From top right to bottom left
          while(x > rect.left || y < rect.bottom) {
            if (element.contains(efp(x,y))) {
              flag = true;
              break;
            }
            if(x > rect.left) { x--; }
            if(y < rect.bottom) { y++; }
          }
        }
      }
    }
    return flag;
}

// Check multiple elements visibility
document.getElementById('container').addEventListener("scroll", function() {
	var elementList = document.getElementsByClassName("element");
  var console = document.getElementById('console');
	for (var i=0; i < elementList.length; i++) {
  	// I did not define parent so it will be element's parent
    if (isVisible(elementList[i])) {
  		console.innerHTML = "Element with id[" + elementList[i].id + "] is visible!";
      break;
    } else {
    	console.innerHTML = "Element with id[" + elementList[i].id + "] is hidden!";
    }
  }
});

// Dynamically added elements
for(var i=4; i <= 6; i++) {
  var newElement = document.createElement("div");
  newElement.id = "element" + i;
  newElement.classList.add("element");
  document.getElementById('container').appendChild(newElement);
}
#console { background-color: yellow; }
#container {
  width: 300px;
  height: 100px;
  background-color: lightblue;
  overflow-y: auto;
  padding-top: 150px;
  margin: 45px;
}
.element {
  margin: 400px;
  width: 400px;
  height: 320px;
  background-color: green;
}
#element3 {
  position: relative;
  margin: 40px;
  width: 720px;
  height: 520px;
  background-color: green;
}
#element3::before {
  content: "";
  position: absolute;
  top: -10px;
  left: -10px;
  margin: 0px;
  width: 740px;
  height: 540px;
  border: 5px dotted green;
  background: transparent;
}
<div id="console"></div>
<div id="container">
    <div id="element1" class="element"></div>
    <div id="element2" class="element"></div>
    <div id="element3" class="element"></div>
</div>

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

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

function isVisible(element, parent, crossSearchAlgorithm) {
    var rect = element.getBoundingClientRect(),
    		prect = (parent != undefined) ? parent.getBoundingClientRect() : element.parentNode.getBoundingClientRect(),
        csa = (crossSearchAlgorithm != undefined) ? crossSearchAlgorithm : false,
        efp = function (x, y) { return document.elementFromPoint(x, y) };
    // Return false if it's not in the viewport
    if (rect.right < prect.left || rect.bottom < prect.top || rect.left > prect.right || rect.top > prect.bottom) {
        return false;
    }
    var flag = false;
    // Return true if left to right any border pixel reached 
    for (var x = rect.left; x < rect.right; x++) {
    	if (element.contains(efp(rect.top, x)) || element.contains(efp(rect.bottom, x))) {
        flag = true;
        break;
      }
    }
    // Return true if top to bottom any border pixel reached 
    if (flag == false) {
      for (var y = rect.top; y < rect.bottom; y++) {
        if (element.contains(efp(rect.left, y)) || element.contains(efp(rect.right, y))) {
          flag = true;
          break;
        }
      }
    }
    if(csa) {
      // Another algorithm to check if element is centered and bigger than viewport
      if (flag == false) {
        var x = rect.left;
        var y = rect.top;
        // From top left to bottom right
        while(x < rect.right || y < rect.bottom) {
          if (element.contains(efp(x,y))) {
            flag = true;
            break;
          }
          if(x < rect.right) { x++; }
          if(y < rect.bottom) { y++; }
        }
        if (flag == false) {
          x = rect.right;
          y = rect.top;
          // From top right to bottom left
          while(x > rect.left || y < rect.bottom) {
            if (element.contains(efp(x,y))) {
              flag = true;
              break;
            }
            if(x > rect.left) { x--; }
            if(y < rect.bottom) { y++; }
          }
        }
      }
    }
    return flag;
}

// Check multiple elements visibility
document.getElementById('container').addEventListener("scroll", function() {
	var elementList = document.getElementsByClassName("element");
  var console = document.getElementById('console');
	for (var i=0; i < elementList.length; i++) {
  	// I did not define parent so it will be element's parent
    // and It will do crossSearchAlgorithm
    if (isVisible(elementList[i],null,true)) {
  		console.innerHTML = "Element with id[" + elementList[i].id + "] is visible!";
      break;
    } else {
    	console.innerHTML = "Element with id[" + elementList[i].id + "] is hidden!";
    }
  }
});
// Dynamically added elements
for(var i=4; i <= 6; i++) {
  var newElement = document.createElement("div");
  newElement.id = "element" + i;
  newElement.classList.add("element");
  document.getElementById('container').appendChild(newElement);
}
#console { background-color: yellow; }
#container {
  width: 300px;
  height: 100px;
  background-color: lightblue;
  overflow-y: auto;
  padding-top: 150px;
  margin: 45px;
}
.element {
  margin: 400px;
  width: 400px;
  height: 320px;
  background-color: green;
}
#element3 {
  position: relative;
  margin: 40px;
  width: 720px;
  height: 520px;
  background-color: green;
}
#element3::before {
  content: "";
  position: absolute;
  top: -10px;
  left: -10px;
  margin: 0px;
  width: 740px;
  height: 540px;
  border: 5px dotted green;
  background: transparent;
}
<div id="console"></div>
<div id="container">
    <div id="element1" class="element"></div>
    <div id="element2" class="element"></div>
    <div id="element3" class="element"></div>
</div>

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

If I had more time this could be improved even further to create a new library for those in need.

Special thanks to @Andy E for providing this perspective to me.

Important Edit: This code is made for more precise info if any part of element 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.




回答19:


Checks if 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} 
}



回答20:


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 IE 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.');
   }
};

Hope this helps someone :-)




回答21:


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
    );
}



回答22:


As simpler as it can get IMO:

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



回答23:


Simplest solution as the compatibility of Element.getBoundingClientRect() has become perfect:

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



回答24:


The accepted answers don't work when zooming in 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);



回答25:


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;
    }

}



回答26:


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 i.e. overTop or overBottom - just should get the drift...



来源：https://stackoverflow.com/questions/24136530/how-to-know-if-an-element-is-actually-appeared-in-browser-and-can-seen-by-human

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