ngx-progressive-image-loader

Support Angular >=6.0.0

Demo

stackblitz.com

Features

• No other JS dependency. Just Angular

• Use IntersectionObserver to determine the timing to load the image

• Support image and picture

• Preserve space to avoid dom reflow

• Show small default loading image with fading transition

• Load image directly for spider (SEO friendly) or non-supported browsers

• Aggressive Loading. Able to continue to load even if images haven't got intersected when the concurrently loading count is lower than a certain value. (after 4.0.0)

Install

npm install ngx-progressive-image-loader --save

Open your module file e.g app.module.ts and update imports array

import { NgxProgressiveImageLoaderModule, IImageLoaderOptions } from 'ngx-progressive-image-loader';
...
imports: [
...
     NgxProgressiveImageLoaderModule.forRoot(<IImageLoaderOptions>{
      // rootMargin must be specified in pixels or percent
      rootMargin: '30px',
      threshold: 0.1,
      // css filter
      filter: 'blur(3px) drop-shadow(0 0 0.75rem crimson)',
      // image width / height ratio for image holder
      imageRatio: 16 / 9,
      // loading image in placeholder. Can be URL or base64
      placeholderImageSrc:
        // tslint:disable-next-line:max-line-length
        'data:image/svg+xml;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIHZpZXdCb3g9IjAgMCAyNTAgMjUwIj4KICA8cGF0aCBmaWxsPSIjZGQwMDMxIiBkPSJNMTI1IDMwTDMxLjkgNjMuMmwxNC4yIDEyMy4xTDEyNSAyMzBsNzguOS00My43IDE0LjItMTIzLjF6Ii8+CiAgPHBhdGggZmlsbD0iI2MzMDAyZiIgZD0iTTEyNSAzMHYyMi4yLS4xVjIzMGw3OC45LTQzLjcgMTQuMi0xMjMuMUwxMjUgMzB6Ii8+CiAgPHBhdGggZD0iTTEyNSA1Mi4xTDY2LjggMTgyLjZoMjEuN2wxMS43LTI5LjJoNDkuNGwxMS43IDI5LjJIMTgzTDEyNSA1Mi4xem0xNyA4My4zaC0zNGwxNy00MC45IDE3IDQwLjl6IiBmaWxsPSIjZmZmIi8+Cjwvc3ZnPgo='
    })
...
]

Add style to your global scss

@import '~ngx-progressive-image-loader/ngx-progressive-image-loader';

$scale: 0.5; // the scale of loading image in place holder
$transition: opacity 1s linear; // the transition of loading image in place holder, you could try: opacity .3s ease
@include progressive-image-loader($scale, $transition);

Usage

• with img

<ngx-progressive-image-loader>
  <ngx-image-placeholder>
    <!-- ngx-image-placeholder is optional -->
    <img [src]="'/assets/Avengers1.jpg'" alt="" ngxProgressiveImage />
  </ngx-image-placeholder>
  <img src="/assets/Avengers2.jpg" alt="" ngxProgressiveImage />
</ngx-progressive-image-loader>

• with img + srcset

<ngx-progressive-image-loader>
  <img
    [src]="'/assets/Avengers6.jpg'"
    [srcset]="'/assets/Avengers6.jpg 800w,/assets/Avengers7.jpg 1366w'"
    size="(max-width: 1000px) 100vw, 100vw"
    ngxProgressiveImage
  />
</ngx-progressive-image-loader>

• with picture element

<ngx-progressive-image-loader>
  <picture ngxProgressiveImage>
    <source [srcset]="'/assets/Avengers4.jpg'" media="(max-width: 1000px)" />
    <source [srcset]="'/assets/Avengers5.jpg'" media="(min-width: 1000px)" />
    <img [src]="'/assets/Avengers4.jpg'" alt="My default image" />
  </picture>
</ngx-progressive-image-loader>

Configuration for IImageLoaderOptions

Intersection_observer_options

• 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). 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.

• filter

  If you want to set more filter. It uses the input string as css filter.

• placeholderImageSrc

  src for loading image. It works just like src, takes base64 or url.

• imageRatio

  image width / height

For ngx-image-placeholder component, it takes

• imageRatio

• placeholderImageSrc

(after 3.0.0, you can set imageRatio and placeholderImageSrc directly on ngxProgressiveImage and spare ngx-image-placeholder layer)

For ngx-progressive-image-loader component, it takes

• imageRatio

• placeholderImageSrc

• filter

• isAggressiveLoading: boolean; default to true; Set to true to enable Aggressive Loading feature. (after 4.0.0)

• concurrentLoading: number; default t0 4; Decided at least how many concurrent loading when Aggressive Loading is enabled

For ngxProgressiveImage directive, (only for image or source elements)

• imageRatio

• placeholderImageSrc

• noPlaceholder: boolean; default to false, set to true will skip image placeholder

Build project

npm i

npm run build

To run demo code locally

npm run start

Browser Compatibility

Browsers don't support Intersection Observer API will not work as expect. It will load images like old time.

Use pollyfill like below might make it work.

<script src="https://polyfill.io/v2/polyfill.min.js?features=IntersectionObserver"></script>

Contributing

• Your commits conform to the conventions established here

Troubleshooting

Please ask your general questions at https://stackoverflow.com

Shoutouts 🙏

This project was generated with Angular CLI version 6.2.0 beta 02.

Kudos to the following authors:

https://deanhume.com/lazy-loading-images-using-intersection-observer/

https://www.voorhoede.nl/en/blog/say-no-to-image-reflow/

https://jmperezperez.com/medium-image-progressive-loading-placeholder/

https://github.com/verlok/lazyload for detecting spider

And my wife and my child to let me work on a weekend for this.

Big thanks to BrowserStack for letting the maintainers use their service to debug browser issues.