ng-lazyload-image

Lazy image loader for Angular ≥ v2

About 150 loc and no dependencies (except for angular and rxjs of course)

Demo: http://tjoskar.github.io/ng-lazyload-image/

Requirement

The browser you targeting need to have support of WeakMap and String.prototype.includes. If you need to support an older browser (like IE) you will need to include polyfill for WeakMap and String.prototype.includes (see https://github.com/zloirock/core-js for example).

Installation

$ npm install ng-lazyload-image --save

And then include it in your module (see app.module.ts):

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { LazyLoadImageModule } from 'ng-lazyload-image';
import { AppComponent } from './app.component';

@NgModule({
    declarations: [ AppComponent ],
    imports: [ BrowserModule, LazyLoadImageModule ],
    bootstrap: [ AppComponent ]
})
export class MyAppModule {}

Usages

import { Component } from '@angular/core';

@Component({
    selector: 'image',
    template: `
        <img [defaultImage]="defaultImage" [lazyLoad]="image" [offset]="offset">
    `
})
class ImageComponent {
    defaultImage = 'https://www.placecage.com/1000/1000';
    image = 'https://images.unsplash.com/photo-1443890923422-7819ed4101c0?fm=jpg';
    offset = 100;
}

It also supports background images, by using backgroundImage:

@Component({
    selector: 'image',
    template: `
        <div [defaultImage]="defaultImage" [lazyLoad]="image" [offset]="offset"></div>
        <!--
        After it has been loaded the div will transform into:
        <div class="ng-lazyloaded" style="background-image: url('https://images.unsplash.com/photo-1443890923422-7819ed4101c0?fm=jpg');"></div>
        -->
    `
})
class ImageComponent {
    defaultImage = 'https://www.placecage.com/1000/1000';
    image = 'https://images.unsplash.com/photo-1443890923422-7819ed4101c0?fm=jpg';
    offset = 100;
}

If using responsive images in a plain <img> tag, you'll need to set the useSrcset attribute to true:

@Component({
    selector: 'image',
    template: `
        <img [defaultImage]="defaultImage"
             [lazyLoad]="images"
             [useSrcset]="true"
             [offset]="offset">
    `
})
class ImageComponent {
    offset = 100;
    defaultImage = 'https://www.placecage.com/1000/1000';
    images = `https://images.unsplash.com/photo-1434725039720-aaad6dd32dfe?fm=jpg 700w,
              https://images.unsplash.com/photo-1437818628339-19ded67ade8e?fm=jpg 1100w`;
}

If using responsive images in a <picture> tag, set the default <img> tag as usual with lazyLoad etc. attributes.
You can use attr.lazyLoad, attr.defaultImage and attr.errorImage attributes for <source> elements.
There's no need to set useSrcset for <source> elements, as srcset is used by default.
A simple example for a <picture> tag:

@Component({
    selector: 'image',
    template: `
        <picture>
            <source media="(min-width: {{ screen_lg }})" [attr.defaultImage]="defaultImage" [attr.lazyLoad]="image2">
            <source media="(min-width: {{ screen_md }})" [attr.defaultImage]="defaultImage" [attr.lazyLoad]="image3">
            <img [defaultImage]="defaultImage"
                 [lazyLoad]="image1"
                 [offset]="offset">
        </picture>
    `
})
class ImageComponent {
    offset = 100;
    screen_lg = '1200px';
    screen_md = '992px';
    defaultImage = 'https://www.placecage.com/1000/1000';
    image1 = 'https://images.unsplash.com/photo-1422004707501-e8dad229e17a?fm=jpg';
    image2 = 'https://images.unsplash.com/photo-1439931444800-9bcc83f804a6?fm=jpg';
    image3 = 'https://images.unsplash.com/photo-1417128281290-30a42da46277?fm=jpg';
}

You can (from 3.3.0) load image async or change the url on the fly, eg.

<img [lazyLoad]="image$ | async">

If you are using Ionic 2 you may need to include your own scroll observable or change the scroll target.

@Component({
    selector: 'page-image',
    template: `
      <ion-content #container padding>
        <img [defaultImage]="https://www.placecage.com/1000/1000" [lazyLoad]="lazyLoadImage" [scrollObservable]="container.ionScroll" />
      </ion-content>
    `
})
export class AboutPage {
    lazyLoadImage = 'https://hd.unsplash.com/photo-1431400445088-1750c997c6b5';
}

In case of using ion-slides in Ionic 2+, you can include your own scroll observable as below.

@Component({
    selector: 'page-image',
    template: `
      <ion-content #container padding>
        <img [defaultImage]="https://www.placecage.com/1000/1000" [lazyLoad]="lazyLoadImage" [scrollObservable]="container.ionSlideWillChange" />
      </ion-content>
    `
})
export class AboutPage {
    lazyLoadImage = 'https://hd.unsplash.com/photo-1431400445088-1750c997c6b5';
}

See example folder for more usages.

FAQ

Q How can I manually trigger the loading of images?

A See: tjoskar#197

Q Does this library work with ionic or some other wrapper for Angular?

A Yes, but ionic and some other library wraps the whole document inside an other div so you might need to create your own scroll listener. https://github.com/tjoskar/ng-lazyload-image/issues?utf8=%E2%9C%93&q=is%3Aissue+Ionic

Q How can I add a transition effect between the default image and the lazy loaded image?

A See: tjoskar#300

Q I can't get it to work with electron. Can you help me?

A Make sure you uses the right file path.

Q I can't get it to work. Can you help me?

A Sure, create an issue and describe your issue in as much detail as possible.

API

lazyLoad

Type: string

Example: https://images.unsplash.com/photo-1443890923422-7819ed4101c0?fm=jpg

The image to be lazy loaded. This image will replace the default image (defaultImage).

defaultImage (optional)

Type: string

Example: https://www.placecage.com/1000/1000

Path to default image. This image will be loaded right away.

You can also use src attribute for img tag to define default image:
<img src="https://www.placecage.com/1000/1000" [lazyLoad]="lazyLoadImage" />

or background-image property for non-image tags:
<div style="background-image: url('https://www.placecage.com/1000/1000');" [lazyLoad]="lazyLoadImage"></div>

errorImage (optional)

Type: string

Example: https://i.imgur.com/XkU4Ajf.png

An image to be loaded if failing to load lazyLoad. Will load the default image (defaultImage) if absent.

offset (optional)

Type: number

Example: 100

Default: 0

Number of px a image should be loaded before it is in view port

scrollTarget (optional)

Type: Element

Example: document.getElementById('my-scroll-container')

Default: window

You will need to set this property if you are using a scroll container and do not propagate the scroll event to window.

scrollObservable (optional)

Type: Observable

Example: Observable.fromEvent(myScrollContainer, 'scroll')

You can pass your own observable if you need more control over the flow. Can be useful if integrating with other frameworks like ionic.

useSrcset (optional)

Type: boolean

Example: true

You can set this to true if you need to lazy load images with srcset attribute, instead of src.
<source> tags are set to use srcset by default, so you don't need to set this option additionaly.

Events

onLoad (optional)

Type: Function: (success: boolean) => void

Example: <img [lazyLoad]="lazyLoadImage" (onLoad)="myCallbackFunction($event)">

You can pass a callback function, which will be called when the image is loaded.

Contributing

See the contributing guide