React lazy load images with IntersectionObserver API

by React

react-simple-img

Smart react image with IntersectionObserver API and animations :clap:

View demo Download Source

? Why this package?

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

Install

yarn add react-simple-img || npm install react-simple-img

Example

Navigate into example folder and install

yarn && yarn start || npm install && npm run start

Tip for the above effect

To generate svg placeholder, please install SQIP to generate placeholders.

Quick start

import { SimpleImg, initSimpleImg } from 'react-simple-img';

initSimpleImg(); // run once at your root component or at file which calls `ReactDOM.render`

export default () => <SimpleImg height={500} src="your image path" />;

API

? initSimpleImg([config]) optional

This function will set up global intersection observer and watch all <SimpleImg /> appear in the viewport through your
entire app

Arguments

  • config: (Object) this argument is optional

    • [root]: The element that is used as the viewport for checking
      visiblity 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.

? SimpleImgProvider([Component], [config])

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

Arguments

  • Component: (Component) react component

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

? 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
placeholder string Placeholder image source (svg, jpg, png...) or css color value (white, linear-gradient(blue, pink))
imgClassName string class for the image itself, which also applied to the placeholder
width number image width apply to original image and placeholder
height number image height apply to original image and placeholder
alt string alt attribute for img tag
wrapperClassName string className for element wrapping img tag
animationDuration number animation duration in seconds
passed as durationSeconds to react-simple-animate
animationEndStyle object
string		 style to transition to
passed as endStyle to react-simple-animate

Advance Example

Set up React Simple Img per page, you can use the following example without initSimpleImg()?

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>
 );

GitHub