How to load images dynamically or lazily when users scrolls them into view

Question

I ve noticed this in numerous  modern  websites  e g  facebook and google image search  where the images below the fold load only when user scrolls down the page enough to bring them inside the visible viewport region  upon view source  the page shows X number of  lt img gt  tags but they are not fetched from the server straight away   What is this technique called  how does it work and in how many browsers does it work  And is there a jQuery plugin that can achieve this behavior with minimum coding   Edit  Bonus  can someone explain if there is a  onScrolledIntoView  or similar event for HTML elements  If not  how do these plugins work

User · Answer

Lazy loading images by attaching listener to scroll events or by making use of setInterval is highly non-performant as each call to getBoundingClientRect() forces the browser to re-layout the entire page and will introduce considerable jank to your website.

Use Lozad.js (just 569 bytes with no dependencies), which uses IntersectionObserver to lazy load images performantly.

User · Answer

There is a pretty nice infinite scroll plugin here  I ve never programmed one myself  but I would imagine this is how it works    An event is bound to the the window scrolling    window  scroll myInfinteScrollFunction    The called function checks if scroll top is greater than the window size  function myInfiniteScrollFunction           if   window  scrollTop        window  height          makeAjaxRequest         An AJAX request is made  specifying which result   to start at  how many to grab  and any other parameters necessary for the data pull     ajax       type   POST       url    myAjaxFile php       data    resultNum   30   numPerPage   50   query    interesting 20icons         success  myInfiniteLoadFunction msg       The ajax returns some  most-likely JSON formatted  content  and passes them into the loadnig function    Hope that makes sense

User · Answer

Im using jQuery Lazy  It took me about 10 minutes to test out and an hour or two to add to most of the image links on one of my websites  CollegeCarePackages com   I have NO  none zero  relationship of any kind to the dev  but it saved me a lot of time and basically helped improve our bounce rate for mobile users and I appreciate it

User · Answer

This Link work for me demo  1 Load the jQuery loadScroll plugin after jQuery library  but before the closing body tag    lt script src  http   ajax googleapis com ajax libs jquery 1 11 2 jquery min js  gt  lt  script gt  lt script src  jQuery loadScroll js  gt  lt  script gt    2 Add the images into your webpage using Html5 data-src attribute  You can also insert placeholders using the regular img s src attribute    lt img data-src  1 jpg  src  Placeholder jpg  alt  Image Alt  gt  lt img data-src  2 jpg  src  Placeholder jpg  alt  Image Alt  gt  lt img data-src  3 jpg  src  Placeholder jpg  alt  Image Alt  gt    3 Call the plugin on the img tags and specify the duration of the     fadeIn effect as your images are come into view     img   loadScroll 500      in ms

User · Answer

The Swiss Army knife of image lazy loading is YUI s ImageLoader   Because there is more to this problem than simply watching the scroll position

User · Answer

Some of the answers here are for infinite page  What Salman is asking is lazy loading of images   Plugin  Demo  EDIT  How do these plugins work   This is a simplified explanation    Find window size and find the position of all images and their sizes If the image is not within the window size  replace it with a placeholder of same size When user scrolls down  and position of image  lt  scroll   window height  the image is loaded

User · Answer

Edit  replaced broken links with archived copies  Dave Artz of AOL gave a great talk on optimization at jQuery Conference Boston last year  AOL uses a tool called Sonar for on-demand loading based on scroll position  Check the code for the particulars of how it compares scrollTop   and others  to the element offset to detect if part or all of the element is visible  jQuery Sonar Dave talks about Sonar in these slides  Sonar starts on slide 46  while the overall  quot load on demand quot  discussion starts on slide 33

User · Answer

I came up with my own basic method which seems to work fine  so far   There s probably a dozen things some of the popular scripts address that I haven t thought of    Note - This solution is fast and easy to implement but of course not great for performance  Definitely look into the new Intersection Observer as mentioned by Apoorv and explained by developers google if performance is an issue   The JQuery    window  scroll function           each    img    function             if     this  attr  data-src    amp  amp    this  offset   top  lt     window  scrollTop       window  height     100                  var source     this  data  src                  this  attr  src   source                 this  removeAttr  data-src                          Sample html code   lt div gt       lt img src    data-src  pathtoyour image1 jpg  gt       lt img src    data-src  pathtoyour image2 jpg  gt       lt img src    data-src  pathtoyour image3 jpg  gt   lt  div gt    Explained  When the page is scrolled each image on the page is checked      this  attr  data-src   - if the image has the attribute data-src  and how far those images are from the bottom of the window      this  offset   top  lt     window  scrollTop       window  height     100   adjust the   100 to whatever you like  - 100 for example   var source     this  data  src    - gets the value of data-src  aka the image url    this  attr  src   source   - puts that value into the src     this  removeAttr  data-src    - removes the data-src attribute  so your browser doesn t waste resources messing with the images that have already loaded   Adding To Existing Code  To convert your html  in an editor just search and replace src   with src    data-src

[javascript] How to load images dynamically (or lazily) when users scrolls them into view

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