Here are the supported values for the `loading` attribute:
- `lazy`: Defer loading of the resource until it reaches a [calculated distance](https://web.dev/articles/browser-level-image-lazy-loading#distance-from-viewport) from the viewport.
- `eager`: Default loading behavior of the browser, which is the same as not including the attribute and means the image is loaded regardless of where it's located on the page. This is the default, but it can be useful to set explicitly if your tooling automatically adds `loading="lazy"` when there's no explicit value, or if your linter complains if it isn't explicitly set.
> [!CAUTION]
> **Caution:** [Don't lazy-load](https://web.dev/articles/browser-level-image-lazy-loading#eager-load-first-images) images that are likely to be in-viewport when the page loads, especially [LCP](https://web.dev/articles/lcp) images.
### Relationship between the `loading` attribute and fetch priority
The `eager` value is an instruction to load the image as usual, without delaying
the load further if the image is off-screen. It doesn't load the image faster
than another image that doesn't have a `loading` attribute.
If you want to increase the fetch priority of an important image (for example,
the LCP image), use [Fetch Priority](https://web.dev/articles/fetch-priority) with
`fetchpriority="high"`.
An image with `loading="lazy"` and `fetchpriority="high"` is still delayed while
it's off-screen, and then fetched with a high priority when it's almost within
the viewport. This combination isn't really necessary because the browser would
likely load that image with high priority anyway.
### Distance-from-viewport thresholds
All images that are immediately viewable without scrolling load normally. Images
far below the device viewport are only fetched when the user scrolls near them.
Chromium's implementation of lazy loading tries to ensure that offscreen images
are loaded early enough that they finish loading by the time the user scrolls
to them by fetching them well before they become visible in the viewport.
> [!NOTE]
> **Note:** Experiments in Chrome on Android suggest that on 4G, 97.5% of lazy-loaded images were fully loaded within 10ms of becoming visible. Even on slow 2G networks, 92.6% of lazy-loaded images were fully loaded within 10ms. This means browser-level lazy loading offers a stable image visibility experience.
The distance threshold varies depending on the following factors:
- The type of image resource being fetched
- The [effective connection type](https://googlechrome.github.io/samples/network-information/)
You can find the default values for the different effective connection types in
the [Chromium source](https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/core/frame/settings.json5;l=963-995).
You can experiment with these different thresholds by
[throttling the network](https://developer.chrome.com/docs/devtools/network/#throttle)
in DevTools.
## Improved data-savings and distance-from-viewport thresholds
In July 2020, Chrome made significant improvements to align the image lazy loading distance-from-viewport thresholds to better meet developer expectations.
On fast connections (4G), we reduced Chrome's distance-from-viewport thresholds from `3000px` to `1250px` and on slower connections (3G or lower), changed the threshold from `4000px` to `2500px`. This change achieves two things:
- `
` element.
## Always eager-load images visible in the first viewport
For images that are visible when the user first loads the page, and especially
for LCP images, use the browser's default eager loading so they can be available
right away. For more information, see [The performance effects of too much lazy-loading](https://web.dev/articles/lcp-lazy-loading).
Use `loading=lazy` only for images outside the initial viewport. The browser
can't lazy-load an image until it knows where the image should be on the page,
which causes them to load more slowly.
## Graceful degradation
Browsers that don't support the `loading` attribute ignore it. They don't get
the benefits of lazy loading, but there's no negative impact from including it.
## FAQ
Some frequently asked questions about browser-level lazy loading.
### Can I automatically lazy-load images in Chrome?
Previously, Chromium automatically lazy-loaded any images that were well suited
to being deferred if [Lite mode](https://blog.chromium.org/2019/04/data-saver-is-now-lite-mode.html)
was enabled on Chrome for Android and the `loading` attribute was either not
provided or set to `loading="auto"`. However,
[Lite mode and `loading="auto"` have been deprecated](https://support.google.com/chrome/thread/151853370/sunsetting-chrome-lite-mode-in-m100-and-older)
and there are no plans to provide automatically lazy-load of images in Chrome.
### Can I change how close an image needs to be to the viewport before it loads?
These values are hardcoded and can't be changed through the API. However, they
might change in the future as browsers experiment with different threshold
distances and variables.
### Can CSS background images use the `loading` attribute?
No, you can only use it with `` tags.
### Can `loading` work with images in the viewport that aren't immediately visible?
Using `loading="lazy"` *can* prevent images being loaded when they aren't
visible but are within the [calculated distance](https://web.dev/articles/browser-level-image-lazy-loading#distance-from-viewport).
These images might be behind a carousel or hidden by CSS for certain screen
sizes. For example, Chrome, Safari, and Firefox don't load images using
`display: none;` styling, either on the image element or on a parent
element. However, other image hiding techniques, such as using `opacity:0`
styling, still cause the browser to load the image. Always test your
implementation thoroughly to make sure it's acting as intended.
Chrome 121 changed the behavior for horizontal-scrolling images like carousels. These now use the same thresholds as vertical scrolling. This means for the carousel use case, images will be loaded before they visible in the viewport. This means the image loading is less likely to be noticeable to the user, but at the cost of more downloads. Use [the Horizontal Lazy Loading demo](https://chrome.dev/horizontal-lazy-loading/) to compare behaviour in Chrome versus Safari and Firefox.
### What if I'm already using a third-party library or a script to lazy-load images?
With full support of lazy loading built into modern browsers, you probably don't
need a third-party library or script to lazy-load images.
One reason to continue to use a third-party library alongside `loading="lazy"`
is to provide a polyfill for browsers that don't support the attribute, or to
have more control over when lazy loading is triggered.
### How do I handle browsers that don't support lazy loading?
Browser-level image lazy loading is well supported across all the major browsers and is recommended for most use cases, to remove the need for extra dependencies on JavaScript.
However, if you have a need to support more browsers or want to have more control over lazy-loading thresholds then you can use a third-party library to lazy-load images on your site.
You can use the `loading` property to detect whether a browser supports the
feature:
if ('loading' in HTMLImageElement.prototype) {
// supported in browser
} else {
// fetch polyfill/third-party library
}
For example, [lazysizes](https://github.com/aFarkas/lazysizes) is a popular
JavaScript lazy loading library. You can detect support for the `loading`
attribute to load lazysizes as a fallback library only when `loading` isn't
supported. This works as follows:
- Replace `` with `` to avoid an eager load in unsupported browsers. If the `loading` attribute is supported, swap `data-src` for `src`.
- If `loading` isn't supported, load a fallback from lazysizes and initiate it, using the `lazyload` class to indicate which images to lazy-load:
Here's a [demo](https://lazy-loading.firebaseapp.com/lazy_loading_lib.html) of
this pattern. Try it in an older browser to see the fallback in action.
> [!NOTE]
> **Note:** The lazysizes library also provides a [loading plugin](https://github.com/aFarkas/lazysizes/tree/gh-pages/plugins/native-loading) that uses browser-level lazy loading when available but falls back to the library's custom behavior when needed.
### Is lazy loading for iframes also supported in browsers?
Browser Support
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