vanilla lazyload Download - vanilla lazyload Source code download

LazyLoad is a lightweight (2.4 kB) and flexible script that speeds up your web application by deferring the loading of your below-the-fold images, animated SVGs, videos and iframes to when they will enter the viewport. It's written in plain "vanilla" JavaScript, it leverages the IntersectionObserver API, it supports responsive images, it optimizes your website for slower connections, and can enable native lazy loading. See all features for more.

➡️ Jump to: ?‍ Getting started - HTML - ?‍ Getting started - Script - ? Recipes - Demos - ? Tips & tricks - ? API - ? All features compared

Love this project? ? Buy me a coffee!

?‍ Getting started - HTML

In order to make your content be loaded by LazyLoad, you must use some data- attributes instead of the actual attributes. Examples below.

Lazy image:

<img alt="A lazy image" class="lazy" data-src="lazy.jpg" />

Lazy image with low quality placeholder:

<img alt="A lazy image" class="lazy" src="lazy-lowQuality.jpg" data-src="lazy.jpg" />

Lazy responsive image with `srcset` and `sizes`:

<img
  alt="A lazy image"
  class="lazy"
  data-src="lazy.jpg"
  data-srcset="lazy_400.jpg 400w, 
    lazy_800.jpg 800w"
  data-sizes="100w"
/>

To have a low quality placeholder, add the src attribute pointing to a very small version of the image. E.g. src="lazy_10.jpg".

Lazy responsive image with hi-dpi support using the `picture` tag:

<picture>
  <source media="(min-width: 1200px)" data-srcset="lazy_1200.jpg 1x, lazy_2400.jpg 2x" />
  <source media="(min-width: 800px)" data-srcset="lazy_800.jpg 1x, lazy_1600.jpg 2x" />
  <img alt="A lazy image" class="lazy" data-src="lazy.jpg" />
</picture>

To have a low quality placeholder, add the src attribute pointing to a very small version of the image to the img tag. E.g. src="lazy_10.jpg".

Lazy responsive image with automatic WebP format selection, using the `picture` tag:

<picture>
  <source
    type="image/webp"
    data-srcset="lazy_400.webp 400w, 
      lazy_800.webp 800w"
    data-sizes="100w"
  />
  <img
    alt="A lazy image"
    class="lazy"
    data-src="lazy.jpg"
    data-srcset="lazy_400.jpg 400w, 
      lazy_800.jpg 800w"
    data-sizes="100w"
  />
</picture>

To have a low quality placeholder, add the src attribute pointing to a very small version of the image to the img tag. E.g. src="lazy_10.jpg".

Lazy background image

IMPORTANT NOTE: To display content images on your pages, always use the img tag. This would benefit the SEO and the accessibility of your website. To understand if your images are content or background, ask yourself: "would my website user like to see those images when printing out the page?". If the answer is "yes", then your images are content images and you should avoid using background images to display them.

Single background image:

<div class="lazy" data-bg="lazy.jpg"></div>

Single background, with HiDPI screen support:

<div class="lazy" data-bg="lazy.jpg" data-bg-hidpi="[email protected]"></div>

Multiple backgrounds:

<div
  class="lazy"
  data-bg-multi="url(lazy-head.jpg), 
    url(lazy-body.jpg), 
    linear-gradient(#fff, #ccc)"
>
  ...
</div>

Multiple backgrounds, HiDPI screen support:

<div
  class="lazy"
  data-bg-multi="url(lazy-head.jpg),
    url(lazy-body.jpg),
    linear-gradient(#fff, #ccc)"
  data-bg-multi-hidpi="url([email protected]),
    url([email protected]),
    linear-gradient(#fff, #ccc)"
>
  ...
</div>

Backgrounds with `image-set`:

<div class="lazy" data-bg-set="url('[email protected]') 1x, url('[email protected]') 2x">...</div>

Multiple backgrounds with `image-set`:

<div
  class="lazy"
  data-bg-set="
    url('[email protected]') 1x, url('[email protected]') 2x | 
    url('[email protected]') 1x, url('[email protected]') 2x
  "
>
  ...
</div>

Lazy animated SVG

<object class="lazy" type="image/svg+xml" data-src="lazy.svg"></object>

Lazy video

<video class="lazy" controls width="620" data-src="lazy.mp4" data-poster="lazy.jpg">
  <source type="video/mp4" data-src="lazy.mp4" />
  <source type="video/ogg" data-src="lazy.ogg" />
  <source type="video/avi" data-src="lazy.avi" />
</video>

Please note that the video poster can be lazily loaded too.

Lazy iframe

<iframe class="lazy" data-src="lazyFrame.html"></iframe>

Love this project? ? Buy me a coffee!

?‍ Getting started - Script

The latest, recommended version of LazyLoad is 19.1.3. Note that if you need to support Internet Explorer 11, you need to use version 17.9.0 or below.

Quickly understand how to upgrade from a previous version reading the practical upgrade guide.

The simple, easiest way

The easiest way to use LazyLoad is to include the script from a CDN.

<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/lazyload.min.js"></script>

OR, if you prefer to import it as an ES module:

<script type="module">
  import LazyLoad from "https://cdn.jsdelivr.net/npm/[email protected]/+esm";
</script>

Then, in your javascript code:

var lazyLoadInstance = new LazyLoad({
  // Your custom settings go here
});

To be sure that DOM for your lazy content is ready when you instantiate LazyLoad, place the script tag right before the closing </body> tag.

If more DOM arrives later, e.g. via an AJAX call, you'll need to call lazyLoadInstance.update(); to make LazyLoad check the DOM again.

lazyLoadInstance.update();

Using an `async` script

If you prefer, it's possible to include LazyLoad's script using async script and initialize it as soon as it's loaded.

To do so, you must define the options before including the script. You can pass:

{} an object to get a single instance of LazyLoad
[{}, {}] an array of objects to get multiple instances of LazyLoad, each one with different options.

<script>
  // Set the options globally
  // to make LazyLoad self-initialize
  window.lazyLoadOptions = {
    // Your custom settings go here
  };
</script>

Then include the script.

<script
  async
  src="https://cdn.jsdelivr.net/npm/[email protected]/dist/lazyload.min.js"
></script>

Possibly place the script tag right before the closing </body> tag. If you can't do that, LazyLoad could be executed before the browser has loaded all the DOM, and you'll need to call its update() method to make it check the DOM again.

Using an `async` script + getting the instance reference

Same as above, but you must put the addEventListener code shown below before including the async script.

<script>
  // Set the options globally
  // to make LazyLoad self-initialize
  window.lazyLoadOptions = {
    // Your custom settings go here
  };
  // Listen to the initialization event
  // and get the instance of LazyLoad
  window.addEventListener(
    "LazyLoad::Initialized",
    function (event) {
      window.lazyLoadInstance = event.detail.instance;
    },
    false
  );
</script>

Then include the script.

<script
  async
  src="https://cdn.jsdelivr.net/npm/[email protected]/dist/lazyload.min.js"
></script>

Now you'll be able to call its methods, like:

lazyLoadInstance.update();

DEMO - SOURCE ← for a single LazyLoad instance

DEMO - SOURCE ← for multiple LazyLoad instances

Local install

If you prefer to install LazyLoad locally in your project, you can!

Using npm

npm install vanilla-lazyload

Using bower

bower install vanilla-lazyload

Manual download

Download one the latest releases. The files you need are inside the dist folder. If you don't know which one to pick, use lazyload.min.js, or read about bundles.

Local usage

Should you install LazyLoad locally, you can import it as ES module like the following:

import LazyLoad from "vanilla-lazyload";

It's also possible (but unadvised) to use the require commonJS syntax.

More information about bundling LazyLoad with WebPack are available on this specific repo.

Usage with React

Take a look at this example of usage of React with LazyLoad on Sandbox.

This implementation takes the same props that you would normally pass to the img tag, but it renders a lazy image. Feel free to fork and improve it!

Bundles

Inside the dist folder you will find different bundles.

Filename	Module Type	Advantages
`lazyload.min.js`	UMD (Universal Module Definition)	Works pretty much everywhere, even in common-js contexts
`lazyload.iife.min.js`	IIFE (Immediately Invoked Function Expression)	Works as in-page `<script src="...">`, ~0.5kb smaller than UMD version
`esm/lazyload.js`	ES Module	Exports `LazyLoad` so you can import it in your project both using `<script type="module" src="...">` and a bundler like WebPack or Rollup

Love this project? ? Buy me a coffee!

? Recipes

This is the section where you can find ready to copy & paste code for your convenience.

Hide alt text and empty image

Use case: when your lazily loaded images show their alt text and the empty image icon before loading.

CSS

img:not([src]):not([srcset]) {
  visibility: hidden;
}

Just that, really.

Image errors handling

Use case: when you want to prevent showing unexisting/broken images on your website.

Javascript

var myLazyLoad = new LazyLoad({
  // Other options here...
  callback_error: (img) => {
    // Use the following line only if your images have the `srcset` attribute
    img.setAttribute("srcset", "[email protected] 1x, [email protected] 2x");
    img.setAttribute("src", "[email protected]");
  }
});

NOTE: if the error was generated by a network down (navigator if temporarily offline), vanilla-lazyload will try and load the images again when the network becomes available again.

EXAMPLE - API

Dynamic content

Use case: when you want to lazily load images, but the number of images change in the scrolling area changes, maybe because they are added asynchronously.

Javascript

var myLazyLoad = new LazyLoad();
// After your content has changed...
myLazyLoad.update();

DEMO - SOURCE - API

Mixed native and JS-based lazy loading

Use case: you want to use the use_native option to delegate the loading of images, iframes and videos to the browsers engine where supported, but you also want to lazily load background images.

HTML

<img class="lazy" alt="A lazy image" data-src="lazy.jpg" />
<iframe class="lazy" data-src="lazyFrame.html"></iframe>
<video class="lazy" controls data-src="lazy.mp4" data-poster="lazy.jpg">...</video>
<object class="lazy" type="image/svg+xml" data-src="lazy.svg"></object>
<div class="lazy" data-bg="lazy.jpg"></div>

Javascript

// Instance using native lazy loading
const lazyContent = new LazyLoad({
  use_native: true // <-- there you go
});

// Instance without native lazy loading
const lazyBackground = new LazyLoad({
  // DON'T PASS use_native: true HERE
});

DEMO - SOURCE - API

Scrolling panel(s)

Use case: when your scrolling container is not the main browser window, but a scrolling container.

HTML

<div class="scrollingPanel">
  <!-- Set of images -->
</div>

Javascript

var myLazyLoad = new LazyLoad({
  container: document.querySelector(".scrollingPanel")
});

DEMO - SOURCE - API

If you have multiple scrolling panels, you can use the following markup and code.

HTML

<div id="scrollingPanel1" class="scrollingPanel">
  <!-- Set of images -->
</div>
<div id="scrollingPanel2" class="scrollingPanel">
  <!-- Set of images -->
</div>

Javascript

var myLazyLoad1 = new LazyLoad({
  container: document.getElementById("scrollingPanel1")
});
var myLazyLoad2 = new LazyLoad({
  container: document.getElementById("scrollingPanel2")
});

DEMO - SOURCE - API

Lazy functions

Use case: when you want to execute arbitrary scripts or functions when given elements enter the viewport

HTML

<div class="lazy" data-lazy-function="foo">...</div>
<div class="lazy" data-lazy-function="bar">...</div>
<div class="lazy" data-lazy-function="buzz">...</div>
<div class="lazy" data-lazy-function="booya">...</div>

// It's a best practice to scope the function names inside a namespace like `lazyFunctions`.
window.lazyFunctions = {
  foo: function (element) {
    element.style.color = "red";
    console.log("foo");
  },
  bar: function (element) {
    element.remove(element);
    console.log("bar");
  },
  buzz: function (element) {
    var span = document.createElement("span");
    span.innerText = " - buzz!";
    element.appendChild(span);
    console.log("buzz");
  },
  booya: function (element) {
    element.classList.add("boo");
    console.log("booya");
  }
};

function executeLazyFunction(element) {
  var lazyFunctionName = element.getAttribute("data-lazy-function");
  var lazyFunction = window.lazyFunctions[lazyFunctionName];
  if (!lazyFunction) return;
  lazyFunction(element);
}

var ll = new LazyLoad({
  unobserve_entered: true, // <- Avoid executing the function multiple times
  callback_enter: executeLazyFunction // Assigning the function defined above
});

Use unobserve_entered to avoid executing the function multiple times.

That's it. Whenever an element with the data-lazy-function attribute enters the viewport, LazyLoad calls the executeLazyScript function, which gets the function name from the data-lazy-function attribute itself and executes it.

DEMO - SOURCE - API

Lazy initialization of multiple LazyLoad instances

Use case: when you have a lot of horizontally scrolling containers and you want to instantiate a LazyLoad instance on them, but only when they entered the viewport.

HTML

<div class="horizContainer">
  <img
    src=""
    alt="Row 01, col 01"
    data-src="https://placeholdit.imgix.net/~text?txtsize=19&amp;txt=row_01_col_01&amp;w=200&amp;h=200"
  />
  <img
    src=""
    alt="Row 01, col 02"
    data-src="https://placeholdit.imgix.net/~text?txtsize=19&amp;txt=row_01_col_02&amp;w=200&amp;h=200"
  />
  <!-- ... -->
</div>
<div class="horizContainer">
  <img
    src=""
    alt="Row 02, col 01"
    data-src="https://placeholdit.imgix.net/~text?txtsize=19&amp;txt=row_02_col_01&amp;w=200&amp;h=200"
  />
  <img
    src=""
    alt="Row 02, col 02"
    data-src="https://placeholdit.imgix.net/~text?txtsize=19&amp;txt=row_02_col_02&amp;w=200&amp;h=200"
  />
  <!-- ... -->
</div>

Javascript

var lazyLoadInstances = [];

var initOneLazyLoad = function (horizContainerElement) {
  // When the .horizContainer element enters the viewport,
  // instantiate a new LazyLoad on the horizContainerElement
  var oneLL = new LazyLoad({
    container: horizContainerElement
  });
  // Optionally push it in the lazyLoadInstances
  // array to keep track of the instances
  lazyLoadInstances.push(oneLL);
};

// The "lazyLazy" instance of lazyload is used to check
// when the .horizContainer divs enter the viewport
var lazyLazy = new LazyLoad({
  elements_selector: ".horizContainer",
  callback_enter: initOneLazyLoad,
  unobserve_entered: true // Stop observing .horizContainer(s) after they entered
});

That's it. Whenever a .horizContainer element enters the viewport, LazyLoad calls the initOneLazyLoad function, which creates a new instance of LazyLoad on the .horizContainer element.

DEMO - SOURCE - API

Love this project? ? Buy me a coffee!

Demos

Didn't find the recipe that exactly matches your case? We have demos!

The demos folder contains 30+ use cases of vanilla-lazyload. You might find there what you're looking for.

Type	Title	Code	Demo
Content	Simple lazy loaded images, not using any placeholder	Code	Live
Content	Lazy images that use an inline SVG as a placeholder	Code	Live
Content	Lazy images that use an external SVG file as a placeholder	Code	Live
Content	Lazy responsive images with `srcset`	Code	Live
Content	Lazy responsive images with the `<picture>` tag and the `media` attribute (art direction)	Code	Live
Content	Lazy responsive images with `srcset` and `sizes` (using `data-sizes`)	Code	Live
Content	Lazy responsive images with `srcset` and `sizes` (using plain `sizes`)	Code	Live
Content	Lazy video with multiple `<source>` tags, different preload options, NO autoplay	Code	Live
Content	Lazy video with multiple `<source>` tags, different preload options, WITH autoplay	Code	Live
Content	Lazy loading background images	Code	Live
Content	Lazy loading multiple background images	Code	Live
Content	Lazy loading background images with `image-set()`	Code	Live
Content	Lazy loading iframes	Code	Live
Content	Lazy loading animated SVGs and PDF files	Code	Live
Content	Lazy WebP images with the `<picture>` tag and the `type` attribute for WebP	Code	Live
Loading	Asynchronous loading LazyLoad with `<script async>`	Code	Live
Loading	Asynchronous loading multiple LazyLoad instances with `<script async>`	Code	Live
Error	Test error loading behaviour when `restore_on_error` is `false`	Code	Live
Error	Test error loading behaviour when `restore_on_error` is `true`	Code	Live
Technique	Fade in images as they load	Code	Live
Technique	Lazy load images in CSS-only horizontal sliders (Netflix style)	Code	Live
Technique	Lazily create Swiper instances and lazily load Swiper images	Code	Live
Technique	Lazily execute functions as specific elements enter the viewport	Code	Live
Technique	How to manage the print of a page with lazy images	Code	Live
Technique	A popup layer containing lazy images in a scrolling container	Code	Live
Settings	Multiple scrolling containers	Code	Live
Settings	Single scrolling container	Code	Live
Methods	How to `restore()` DOM to its original state, and/or `destroy()` LazyLoad	Code	Live
Methods	Adding dynamic content, then `update()` LazyLoad	Code	Live
Methods	Adding dynamic content, then `update()` LazyLoad passing a NodeSet of elements	Code	Live
Methods	Load punctual images using the `load()` method	Code	Live
Methods	Load all images at once using `loadAll()`	Code	Live
Test	Test for multiple thresholds	Code	Live
Test	Test behaviour with hidden images	Code	Live
Test	Test performance, lazy loading of hundreds of images	Code	Live
Native	Test the native lazy loading of images WITHOUT any line of javascript, not even this script	Code	Live
Native	Test the native lazy loading of images conditionally using the `use_native` option (see API)	Code	Live

Love this project? ? Buy me a coffee!

? Tips & tricks

Expand

vanilla lazyload

?‍ Getting started - HTML

Lazy image:

Lazy image with low quality placeholder:

Lazy responsive image with srcset and sizes:

Lazy responsive image with hi-dpi support using the picture tag:

Lazy responsive image with automatic WebP format selection, using the picture tag:

Lazy background image

Single background image:

Single background, with HiDPI screen support:

Multiple backgrounds:

Multiple backgrounds, HiDPI screen support:

Backgrounds with image-set:

Multiple backgrounds with image-set:

Lazy animated SVG

Lazy video

Lazy iframe

?‍ Getting started - Script

The simple, easiest way

Using an async script

Using an async script + getting the instance reference

Local install

Using npm

Using bower

Manual download

Local usage

Usage with React

Bundles

? Recipes

Hide alt text and empty image

Image errors handling

Dynamic content

Mixed native and JS-based lazy loading

Scrolling panel(s)

Lazy functions

Lazy initialization of multiple LazyLoad instances

Demos

? Tips & tricks

Lazy responsive image with `srcset` and `sizes`:

Lazy responsive image with hi-dpi support using the `picture` tag:

Lazy responsive image with automatic WebP format selection, using the `picture` tag:

Backgrounds with `image-set`:

Multiple backgrounds with `image-set`:

Using an `async` script

Using an `async` script + getting the instance reference