Smart react lazy load image with IntersectionObserver API

February 21, 2019 0 Comments

Smart react lazy load image with IntersectionObserver API



Smart react lazy load image with IntersectionObserver API

React lazy load images with IntersectionObserver API and Priority Hints.

Smart react lazy load image with IntersectionObserver API, Priority Hints and animations :clap:

  • Speed up initial page loads by loading only images above the fold
  • Responsive with placeholders and animations
  • Support Priority Hints with importance attribute
  • Smart download logic using IntersectionObserver
  • Simple usage and tiny size


npm install react-simple-img


import { SimpleImg } from 'react-simple-img'; export default () => <SimpleImg height={500} src="your image path" />;


🔗 SimpleImg

Image component working similar with standard img tag and with the following props.

Prop Type Required Description
src string The large image source
srcSet string eg: large.jpg 2x, small.jpg
Reference for examples
sizes string eg: (max-width: 320px) 280px, (max-width: 480px) 440px
Reference for examples
importance string Priority Hints with "low" or "high": set to "high" will load image after load event, otherwise "low" will load images after load event and lazy load with intersection observer
placeholder string Placeholder image source (svg, jpg, png...) or css color value (white, linear-gradient(blue, pink))
applyAspectRatio boolean Image will scale automatically with aspect ratio. Note: width and height will need to be supplied
animationDuration number animation duration in seconds
passed as durationSeconds to react-simple-animate
animationEndStyle Object style to transition to
passed as endStyle to react-simple-animate

🔗 initSimpleImg([config], disableAnimationAfterCache) optional

This function is only required, when you want to customise intersection observer configuration.


  • config: (Object) this argument is optional

    • [root]: The element that is used as the viewport for checking visibility of the target. Must be the ancestor of the target. Defaults

      to the browser viewport if not specified or if null.

  • [rootMargin]: Margin around the root. Can have values similar to the CSS margin property, e.g. "10px 20px 30px 40px" (top, right, bottom, left). If the root element is specified, the values can be percentages. This set of values serves to grow or shrink each side of the root element's bounding box before computing intersections.

    Defaults to all zeros.

  • [threshold]: Either a single number or an array of numbers which indicate at what percentage of the target's visibility the observer's callback should be executed. If you only want to detect when visibility passes the 50% mark, you can use a value of 0.5. If you want the callback run every time visibility passes another 25%, you would specify the array [0, 0.25, 0.5, 0.75, 1]. The default is 0 (meaning as soon as even one pixel is visible, the callback will be run). A value of 1.0 means that the threshold isn't considered passed

    until every pixel is visible.

  • disableAnimationAfterCache: (boolean) this argument is optional

    • if you want to disable the reveal animation after image have been cached

  • 🔗 SimpleImgProvider([Component], [config]) optional

    This high order component will connect all your SimpleImg to be observed per section, and overwrite global config by


    • Component: (Component) react component

    • config: (Object) this argument is optional (same as initSimpleImg config argument)

    Advance Example

    Set up intersection observer config at page level with SimpleImgProvider

    import { SimpleImg, SimpleImgProvider } from 'react-simple-img'; export default () => ( <SimpleImgProvider config={{ threshold: [0.5], // load image when 50 percentage of image in the view port }} > // placeholder background color example <SimpleImg height={500} placeholder="linear-gradient(rgb(30, 87, 153) 0%, rgb(125, 185, 232) 100%)" src="your image path" /> // placeholder background image example <SimpleImg height={500} placeholder="your placeholder svg or image path" src="your image path" /> </SimpleImgProvider>


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