Vue自定义指令结合阿里云OSS优化图片

图片往往在加载前端项目中占大头，如何既不损失图片质量，又提升加载速度呢？

1. 根据显示设备pixelRatio和元素宽高来显示合适图片
2. 略微压缩图片质量
3. 使用webp

注册全局自定义指令

Vue.directive('img-condense', {
  bind: (el, binding, vnode) => {
    let src = el.getAttribute('src')
    let newSrc = compressImg(src, el)
    el.setAttribute('src', newSrc)
  }
})

获取元素宽高和显示设备pixelRatio

let compressImg = (imgUrl, el) => {
  let elStyle = $(el)
  // 获取显示设备 pixelRatio
  let pixelRatio = window.devicePixelRatio
  let elWidth = elStyle.width() * pixelRatio
  let elHeight = elStyle.height() * pixelRatio
  let resize = '/resize'
  if (elWidth) {
    resize += `,w_${elWidth}`
  }
  if (elHeight) {
    resize += `,h_${elHeight}`
  }
})

判断webp

let canUseWebp = document.createElement('canvas').toDataURL('image/webp').indexOf('data:image/webp') == 0
let webp = ''
if (canUseWebp) {
  webp = '/format,webp'
}

质量降低至80%

let ossParam?x-oss-process=image${resize}/auto-orient,1/quality,Q_80/bright,-1${webp}

完整版

<img v-img-condense alt="Vue logo" src="../assets/logo.png">
Vue.directive('img-condense', {
  bind: (el, binding, vnode) => {
    let src = el.getAttribute('src')
    let newSrc = compressImg(src, el)
    el.setAttribute('src', newSrc)
  }
})
let compressImg = (imgUrl, el) => {
  // 如果不是oss 或者已经压缩过的图片直接返回
  if (imgUrl.includes('aliyuncs.com') || imgUrl.indexOf('blob') === 0 || imgUrl.includes('x-oss-process=')){
    return imgUrl  
  }
  // 获取显示设备 pixelRatio
  let pixelRatio = window.devicePixelRatio
  let elWidth = el.width * pixelRatio
  let elHeight = el.height * pixelRatio
  let resize = '/resize'
  if (elWidth) {
    resize += `,w_${elWidth}`
  }
  if (elHeight) {
    resize += `,h_${elHeight}`
  }
  if (!elWidth && !elHeight) {
    resize = ''
  }
  // 判断webp
  let canUseWebp = document.createElement('canvas').toDataURL('image/webp').indexOf('data:image/webp') == 0
  let webp = ''
  if (canUseWebp) {
    webp = '/format,webp'
  }
  return `${imgUrl}?x-oss-process=image${resize}/auto-orient,1/quality,Q_80/bright,-1${webp}`
}