This documentation is for imgix.js version 3.0.0 and up. Those using imgix.js 2.x.x can find documentation in that version's readme and API reference.
Note: If you're looking for a Javascript library just to generate imgix URLs, check out imgix-core-js.
imgix.js allows developers to easily generate responsive images using the srcset and sizes attributes, or the picture element. This lets you write a single image URL that is parsed and used to make images look great at any screen size, by using imgix to process and resize your images on the fly.
Responsive images in the browser, simplified. Pure JavaScript with zero dependencies. About 2 KB minified and gzipped.
Before you get started with imgix.js, it's highly recommended that you read Eric Portis' seminal article on srcset and sizes. This article explains the history of responsive images in responsive design, why they're necessary, and how all these technologies work together to save bandwidth and provide a better experience for users. The primary goal of imgix.js is to make these tools easier for developers to implement, so having an understanding of how they work will significantly improve your imgix.js experience.
Below are some other articles that help explain responsive imagery, and how it can work alongside imgix:
- Using imgix with
<picture>. Discusses the differences between art direction and resolution switching, and provides examples of how to accomplish art direction with imgix. - Responsive Images with
srcsetand imgix. A look into how imgix can work withsrcsetandsizesto serve the right image.
There are several ways to install imgix.js. The appropriate method depends on your project.
- npm:
npm install --save imgix.js - Bower:
bower install --save imgix.js - Manual: Download the latest release of imgix.js, and use
dist/imgix.jsordist/imgix.min.js.
If your build process will re-run dist/imgix.js or dist/imgix.min.js through Browserify, you'll need to add noParse: [require.resolve('imgix.js')] to your Browserify config. If you skip this, Browserify will attempt to re-require imgix.js' dependencies, which have already been inlined.
After you've included imgix.js on your page, it will automatically run once, after the DOMContentLoaded event fires. This will detect and process all img and source tags on the page that are set up to use imgix.js as described in the Usage section of this README.
imgix.js has two important global options:
host: Your imgix hostname (defaults tonull). This enables the use ofix-pathandix-paramsto define images, instead of having to manually type URLs out inix-src. See theix-pathandix-paramssection below for details.useHttps: A boolean (defaults totrue), specifying whether to generatehttporhttps-prefixed URLs.
These configuration options (as well as other options described in the "Advanced Usage" section) can be defined in two ways. The easiest way is to specify them with meta tags in your document's <head>:
<head>
<meta property="ix:host" content="assets.imgix.net">
<meta property="ix:useHttps" content="true">
</head>The other way is to manually set these options on the imgix.config object. Note that these options should be set after loading imgix.js, but before the DOMContentLoaded event is fired on the page:
<script src="imgix.js"></script>
<script>
imgix.config.host = 'assets.imgix.net';
imgix.config.useHttps = false;
</script>Now that everything's installed and set up, you can start adding responsive images to the page. There are a few ways to do this.
The simplest way to use imgix.js is to create an img tag with the ix-src attribute:
<img
ix-src="https://assets.imgix.net/unsplash/hotairballoon.jpg?w=300&h=500&fit=crop&crop=right"
alt="A hot air balloon on a sunny day"
sizes="100vw"
>Please note: 100vw is an appropriate sizes value for a full-bleed image. If your image is not full-bleed, you should use a different value for sizes. Eric Portis' "Srcset and sizes" article goes into depth on how to use the sizes attribute.
This will generate HTML something like the following:
<img
ix-src="https://assets.imgix.net/unsplash/hotairballoon.jpg?w=300&h=500&fit=crop&crop=right"
alt="A hot air balloon on a sunny day"
sizes="100vw"
srcset="
https://assets.imgix.net/unsplash/hotairballoon.jpg?w=100&h=167&fit=crop&crop=right 100w,
https://assets.imgix.net/unsplash/hotairballoon.jpg?w=200&h=333&fit=crop&crop=right 200w,
…
https://assets.imgix.net/unsplash/hotairballoon.jpg?w=2560&h=4267&fit=crop&crop=right 2560w
"
src="https://assets.imgix.net/unsplash/hotairballoon.jpg?w=300&h=500&fit=crop&crop=right"
ix-initialized="ix-initialized"
>Since imgix can generate as many derivative resolutions as needed, imgix.js calculates them programmatically, using the dimensions you specify (note that the w and h params scale appropriately to maintain the correct aspect ratio). All of this information has been placed into the srcset and sizes attributes. Because of this, imgix.js no longer needs to watch or change the img tag, as all responsiveness will be handled automatically by the browser as the page is resized.
If you've configured imgix.js with a global host option, you can use the ix-path and ix-params attributes instead of ix-src. The ix-path attribute is used to specify the path to your image, and the ix-params attribute is used to define the imgix URL API parameters you'd like to apply to your image. Using these two attributes instead of ix-src has several advantages:
ix-paramsautomatically URL/Base64-encodes your specified parameters, as appropriate.ix-paramsis a JSON string, which is easier to read than a URL and can be generated by other tools if necessary.- Not having to re-type
https://my-source.imgix.nethelps keep your code DRY.
Here's how the previous example would be written out using ix-path and ix-params instead of ix-src. Regardless of which method you choose, the end result in-browser will be the same.
<img
ix-path="unsplash/hotairballoon.jpg"
ix-params='{
"w": 300,
"h": 500,
"fit": "crop",
"crop": "right"
}'
alt="A hot air balloon on a sunny day"
>Please note: ix-params must be a valid JSON string. This means that keys and string values must be surrounded by double quotes, e.g., "fit": "crop".
If you need art-directed images, imgix.js plays nicely with the picture tag. This allows you to specify more advanced responsive images, by changing things such as the crop and aspect ratio for different screens. To get started, just construct a picture tag with a source attribute for each art-directed image, and a fallback img tag. If you're new to using the picture tag, you might want to check out our tutorial to learn how it works.
The source tags can be used with ix-src or ix-path and ix-params, just like img tags. The following example will generate HTML that displays Bert and Ernie on small screens, just Bert on medium-sized screens, and just Ernie on large screens.
<picture>
<source
media="(min-width: 880px)"
sizes="430px"
ix-path="imgixjs-demo-page/bertandernie.jpg"
ix-params='{
"w": 300,
"h": 300,
"fit": "crop",
"crop": "left"
}'
>
<source
media="(min-width: 640px)"
sizes="calc(100vw - 20px - 50%)"
ix-path="imgixjs-demo-page/bertandernie.jpg"
ix-params='{
"w": 300,
"h": 300,
"fit": "crop",
"crop": "right"
}'
>
<source
sizes="calc(100vw - 20px)"
ix-path="imgixjs-demo-page/bertandernie.jpg"
ix-params='{
"w": 300,
"h": 100,
"fit": "crop"
}'
>
<img ix-path="imgixjs-demo-page/bertandernie.jpg">
</picture>If you need to display images from multiple imgix Sources, the host option can be overridden on any img or source tag by specifying an ix-host attribute in the tag:
<img
ix-host="a-different-source.imgix.net"
ix-path="unsplash/hotairballoon.jpg"
ix-params='{
"w": 300,
"h": 500,
"fit": "crop",
"crop": "right"
}'
alt="A hot air balloon on a sunny day"
>By default, imgix.js will automatically run as soon as the DOMContentLoaded event fires, immediately processing all img and source tags on the page that are set up to use imgix.js. You can disable this auto-initialization behavior by including the following meta tag in your document's head:
<head>
<meta property="ix:autoInit" content="false">
</head>If you disable auto-initialization as described above, you'll need to manually run imgix.js in order to process the img and source tags on the page. You can do so by simply calling imgix.init().
When calling imgix.init(), you can also pass in a map of options to override the global configuration settings. For example:
imgix.init({
useHttps: false,
host: 'a-different-source.imgix.net'
});Whether imgix.init() is run automatically when the DOMContentLoaded event fires or manually initialized, it will always be idempotent. This means that img and source tags that have already been processed by imgix.js will not be re-processed by subsequent calls.
However, if you would like to re-process all imgix.js-ready img and source tags, you can override the function's idempotency by calling imgix.init() again and passing in the force: true option:
imgix.init({
force: true
})Lazy Loading With lazysizes
If you'd like to lazy load images, we recommend using lazysizes. In order to use imgix.js with lazysizes, you can simply tell it to generate lazysizes-compatible attributes instead of the standard src, srcset, and sizes by changing some configuration settings:
Using <meta> tags:
<head>
<meta property="ix:srcAttribute" content="data-src">
<meta property="ix:srcsetAttribute" content="data-srcset">
<meta property="ix:sizesAttribute" content="data-sizes">
</head>Using JavaScript:
imgix.config.srcAttribute = 'data-src';
imgix.config.srcsetAttribute = 'data-srcset';
imgix.config.sizesAttribute = 'data-sizes';imgix.js defaults to pulling its data from the ix-src, ix-path, ix-params, and ix-host attributes. If you'd like to use custom input attributes, you can specify them by changing some configuration settings. This can be useful if you're concerned about W3C compliance.
Using <meta> tags:
<head>
<meta property="ix:srcInputAttribute" content="data-ix-src">
<meta property="ix:pathInputAttribute" content="data-ix-path">
<meta property="ix:paramsInputAttribute" content="data-ix-params">
<meta property="ix:hostInputAttribute" content="data-ix-host">
</head>Using JavaScript:
imgix.config.srcInputAttribute = 'data-ix-src';
imgix.config.pathInputAttribute = 'data-ix-path';
imgix.config.paramsInputAttribute = 'data-ix-params';
imgix.config.hostInputAttribute = 'data-ix-host';In rare cases, it may be undesirable to have imgix.js modify the src, srcset, or sizes attributes of the <img> elements it's targeting. In such cases, you can override the default behavior by setting some configuration values to null:
Using <meta> tags:
<head>
<meta property="ix:srcAttribute" content="">
<meta property="ix:srcsetAttribute" content="">
<meta property="ix:sizesAttribute" content="">
</head>Using JavaScript:
imgix.config.srcAttribute = null;
imgix.config.srcsetAttribute = null;
imgix.config.sizesAttribute = null;All of imgix's API parameters can be provided as Base64 variants. This is especially useful when providing text for the txt parameter, or URLs for parameters such as mark or blend.
When providing parameters to imgix.js via the ix-params attribute, note that the values for any Base64 variant parameters will be automatically base64-encoded by imgix.js, and can therefore be provided unencoded.
<img
ix-path="unsplash/hotairballoon.jpg"
ix-params='{
"txt64": "Hello, World!"
}'
alt="A hot air balloon on a sunny day"
>When providing a URL with parameters to imgix.js via the ix-src attribute, note that the values for any Base64 variant parameters will not be automatically base64-encoded by imgix.js.
<img
ix-src="https://assets.imgix.net/unsplash/hotairballoon.jpg?txt64=SGVsbG8sIFdvcmxkIQ"
alt="A hot air balloon on a sunny day"
sizes="100vw"
>For security and diagnostic purposes, we default to signing all requests with the language and version of library used to generate the URL. This can be disabled by setting the includeLibraryParam configuration option to false.
Using a <meta> tag:
<head>
<meta property="ix:includeLibraryParam" content="false">
</head>Using JavaScript:
imgix.config.includeLibraryParam = false;- By default, browsers that don't support
srcset,sizes, orpicturewill gracefully fall back to the defaultimgsrcwhen appropriate. If you want to provide a fully-responsive experience for these browsers, imgix.js works great alongside Picturefill! - If you are using Base64 variant params and need IE <= 9 support, we recommend using a polyfill for
atob/btoa, such as Base64.js.
imgix.js was made by imgix. It's licensed under the BSD 2-Clause license (see the license file for more info). Any contribution is absolutely welcome, but please review the contribution guidelines before getting started.
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