vue3+typescript实现图片懒加载插件
github项目地址: github.com/murongg/vue…
求star 与 issues
我文采不好，可能写的文章不咋样，有什么问题可以在留言区评论，我会尽力解答
本项目已经发布到npm
安装：
$ npm i vue3-lazyload
# or
$ yarn add vue3-lazyload
需求分析
img 标签绑定 lazy 属性，类似于
<img src="..." lazy="loading">
<img src="..." lazy="loaded">
<img src="..." lazy="error">
并支持：
img[lazy=loading] {
/*your style here*/
}
img[lazy=error] {
/*your style here*/
}
img[lazy=loaded] {
/*your style here*/
}
支持使用 v-lazy 自定义指令，指定可传入 string/object ，当为 string 时，默认为需要加载的 url，当为 object 时，可传入
src: 当前需要加载的图片 url
loading: 加载状态时所用到的图片
error: 加载失败时所用到的图片
lifecycle: 本次 lazy 的生命周期，替换掉全局生命周期
目录结构
- src
---- index.ts 入口文件，主要用来注册插件
---- lazy.ts 懒加载主要功能
---- types.ts 类型文件，包括 interface/type/enum 等等
---- util.ts 共享工具文件
编写懒加载类
懒加载主要通过 IntersectionObserver对象实现，可能有些浏览器不支持，暂未做兼容。
确定注册插件时传入的参数
export interface LazyOptions {
error?: string; // 加载失败时的图片
loading?: string; // 加载中的图片
observerOptions?: IntersectionObserverInit; // IntersectionObserver 对象传入的第二个参数
log?: boolean; // 是否需要打印日志
lifecycle?: Lifecycle; // 生命周期 hooks
}
export interface ValueFormatterObject {
src: string,
error?: string,
loading?: string,
lifecycle?: Lifecycle;
}
export enum LifecycleEnum {
LOADING = 'loading',
LOADED = 'loaded',
ERROR = 'error'
}
export type Lifecycle = {
[x in LifecycleEnum]?: () => void;
};
确定类的框架
vue3 的 Custom Directives，支持以下 Hook Functions：beforeMount 、mounted、beforeUpdate、updated、beforeUnmount、unmounted，具体释义可以去 vue3 文档查看，目前仅需要用到mounted、updated、unmounted，这三个 Hook。
Lazy 类基础框架代码，lazy.ts：
export default class Lazy {
public options: LazyOptions = {
loading: DEFAULT_LOADING,
error: DEFAULT_ERROR,
observerOptions: DEFAULT_OBSERVER_OPTIONS,
log: true,
lifecycle: {}
};
constructor(options?: LazyOptions) {
this.config(options)
}
/**
* merge config
* assgin 方法在 util.ts 文件内，此文章不在赘述此方法代码，可在后文 github 仓库内查看此代码
* 此方法主要功能是合并两个对象
*
* @param {*} [options={}]
* @memberof Lazy
*/
public config(options = {}): void {
assign(this.options, options)
}
public mount(el: HTMLElement, binding: DirectiveBinding<string | ValueFormatterObject>): void {} // 对应 directive mount hook
public update() {} // 对应 directive update hook
public unmount() {} // 对应 directive unmount hook
}
编写懒加载功能
/**
* mount
*
* @param {HTMLElement} el
* @param {DirectiveBinding<string>} binding
* @memberof Lazy
*/
public mount(el: HTMLElement, binding: DirectiveBinding<string | ValueFormatterObject>): void {
this._image = el
const { src, loading, error, lifecycle } = this._valueFormatter(binding.value)
this._lifecycle(LifecycleEnum.LOADING, lifecycle)
this._image.setAttribute('src', loading || DEFAULT_LOADING)
if (!hasIntersectionObserver) {
this.loadImages(el, src, error, lifecycle)
this._log(() => {
throw new Error('Not support IntersectionObserver!')
})
}
this._initIntersectionObserver(el, src, error, lifecycle)
}
/**
* force loading
*
* @param {HTMLElement} el
* @param {string} src
* @memberof Lazy
*/
public loadImages(el: HTMLElement, src: string, error?: string, lifecycle?: Lifecycle): void {
this._setImageSrc(el, src, error, lifecycle)
}
/**
* set img tag src
*
* @private
* @param {HTMLElement} el
* @param {string} src
* @memberof Lazy
*/
private _setImageSrc(el: HTMLElement, src: string, error?: string, lifecycle?: Lifecycle): void {
const srcset = el.getAttribute('srcset')
if ('img' === el.tagName.toLowerCase()) {
if (src) el.setAttribute('src', src)
if (srcset) el.setAttribute('srcset', srcset)
this._listenImageStatus(el as HTMLImageElement, () => {
this._log(() => {
console.log('Image loaded successfully!')
})
this._lifecycle(LifecycleEnum.LOADED, lifecycle)
}, () => {
// Fix onload trigger twice, clear onload event
// Reload on update
el.onload = null
this._lifecycle(LifecycleEnum.ERROR, lifecycle)
this._observer.disconnect()
if (error) el.setAttribute('src', error)
this._log(() => { throw new Error('Image failed to load!') })
})
} else {
el.style.backgroundImage = 'url(\'' + src + '\')'
}
}
/**
* init IntersectionObserver
*
* @private
* @param {HTMLElement} el
* @param {string} src
* @memberof Lazy
*/
private _initIntersectionObserver(el: HTMLElement, src: string, error?: string, lifecycle?: Lifecycle): void {
const observerOptions = this.options.observerOptions
this._observer = new IntersectionObserver((entries) => {
Array.prototype.forEach.call(entries, (entry) => {
if (entry.isIntersecting) {
this._observer.unobserve(entry.target)
this._setImageSrc(el, src, error, lifecycle)
}
})
}, observerOptions)
this._observer.observe(this._image)
}
/**
* only listen to image status
*
* @private
* @param {string} src
* @param {(string | null)} cors
* @param {() => void} success
* @param {() => void} error
* @memberof Lazy
*/
private _listenImageStatus(image: HTMLImageElement, success: ((this: GlobalEventHandlers, ev: Event) => any) | null, error: OnErrorEventHandler) {
image.onload = success
image.onerror = error
}
/**
* to do it differently for object and string
*
* @public
* @param {(ValueFormatterObject | string)} value
* @returns {*}
* @memberof Lazy
*/
public _valueFormatter(value: ValueFormatterObject | string): ValueFormatterObject {
let src = value as string
let loading = this.options.loading
let error = this.options.error
let lifecycle = this.options.lifecycle
if (isObject(value)) {
src = (value as ValueFormatterObject).src
loading = (value as ValueFormatterObject).loading || this.options.loading
error = (value as ValueFormatterObject).error || this.options.error
lifecycle = ((value as ValueFormatterObject).lifecycle || this.options.lifecycle)
}
return {
src,
loading,
error,
lifecycle
}
}
/**
* log
*
* @param {() => void} callback
* @memberof Lazy
*/
public _log(callback: () => void): void {
if (!this.options.log) {
callback()
}
}
/**
* lifecycle easy
*
* @private
* @param {LifecycleEnum} life
* @param {Lifecycle} [lifecycle]
* @memberof Lazy
*/
private _lifecycle(life: LifecycleEnum, lifecycle?: Lifecycle): void {
switch (life) {
case LifecycleEnum.LOADING:
this._image.setAttribute('lazy', LifecycleEnum.LOADING)
if (lifecycle?.loading) {
lifecycle.loading()
}
break
case LifecycleEnum.LOADED:
this._image.setAttribute('lazy', LifecycleEnum.LOADED)
if (lifecycle?.loaded) {
lifecycle.loaded()
}
break
case LifecycleEnum.ERROR:
this._image.setAttribute('lazy', LifecycleEnum.ERROR)
if (lifecycle?.error) {
lifecycle.error()
}
break
default:
break
}
}
编写 update hook
/**
* update
*
* @param {HTMLElement} el
* @memberof Lazy
*/
public update(el: HTMLElement, binding: DirectiveBinding<string | ValueFormatterObject>): void {
this._observer.unobserve(el)
const { src, error, lifecycle } = this._valueFormatter(binding.value)
this._initIntersectionObserver(el, src, error, lifecycle)
}
编写 unmount hook
/**
* unmount
*
* @param {HTMLElement} el
* @memberof Lazy
*/
public unmount(el: HTMLElement): void {
this._observer.unobserve(el)
}
在 index.ts 编写注册插件需要用到的 install 方法
import Lazy from './lazy'
import { App } from 'vue'
import { LazyOptions } from './types'
export default {
/**
* install plugin
*
* @param {App} Vue
* @param {LazyOptions} options
*/
install (Vue: App, options: LazyOptions): void {
const lazy = new Lazy(options)
Vue.config.globalProperties.$Lazyload = lazy
// 留着备用，为了兼容$Lazyload
// 选项api，可以通过this.$Lazyload获取到Lazy类的实例，组合api我还不知道怎么获取
// 所以通过 provide 来实现此需求
// 使用方式 const useLazylaod = inject('Lazyload')
Vue.provide('Lazyload', lazy)
Vue.directive('lazy', {
mounted: lazy.mount.bind(lazy),
updated: lazy.update.bind(lazy),
unmounted: lazy.unmount.bind(lazy)
})
}
}
使用插件
import { createApp } from 'vue'
import App from './App.vue'
import VueLazyLoad from '../src/index'
const app = createApp(App)
app.use(VueLazyLoad, {
log: true,
lifecycle: {
loading: () => {
console.log('loading')
},
error: () => {
console.log('error')
},
loaded: () => {
console.log('loaded')
}
}
})
app.mount('#app')
App.vue:
<template>
<div class="margin" />
<img v-lazy="'/example/assets/logo.png'" alt="Vue logo" width="100">
<img v-lazy="{src: errorlazy.src, lifecycle: errorlazy.lifecycle}" alt="Vue logo" class="image" width="100">
<button @click="change">
change
</button>
</template>
<script>
import { reactive } from 'vue'
export default {
name: 'App',
setup() {
const errorlazy = reactive({
src: '/example/assets/log1o.png',
lifecycle: {
loading: () => {
console.log('image loading')
},
error: () => {
console.log('image error')
},
loaded: () => {
console.log('image loaded')
}
}
})
const change = () => {
errorlazy.src = 'http://t8.baidu.com/it/u=3571592872,3353494284&fm=79&app=86&size=h300&n=0&g=4n&f=jpeg?sec=1603764281&t=bedd2d52d62e141cbb08c462183601c7'
}
return {
errorlazy,
change
}
}
}
</script>
<style>
.margin {
margin-top: 1000px;
}
.image[lazy=loading] {
background: goldenrod;
}
.image[lazy=error] {
background: red;
}
.image[lazy=loaded] {
background: green;
}
</style>
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