JS将base64图片压缩至指定大小

base64图片压缩至指定大小

1. 在开发中，通常在上传图片时，由于各种限制，需要将上传的图片压缩到某一大小范围内才能上传。在此提供以下方法实现该需求，复制可用。

   /**
    * 压缩图片到指定大小
    * @param baseImg base64图片
    * @param maxSize 单位kb
    */
   export function compressImgBySize (baseImg, maxSize = 200) {
     return new Promise((resolve) => {
       const strLength = baseImg.length
       const fileLength = parseInt(strLength - (strLength / 8) * 2)
       let size = parseInt((fileLength / 1024).toFixed(2))
   
       if (size <= maxSize) {
         resolve(baseImg)
         return
       }
   
       const img = new Image()
       // img.src = 'data:image/jpeg;base64,' + baseImg
       img.src = baseImg
       img.onload = () => {
         const canvas = imgToCanvas(img)
         let resUrl = ''
         let quality = 0.9
         while (size > maxSize && quality > 0) {
           resUrl = canvas.toDataURL('image/jpeg', quality).replace(/^data:image\/\w+;base64,/, '')
           const resLength = resUrl.length
           const resFileLength = parseInt(resLength - (resLength / 8) * 2)
           size = parseInt((resFileLength / 1024).toFixed(2))
           quality = (quality - 0.1).toFixed(1)
         }
         resolve(resUrl)
       }
       img.onerror = () => {
         resolve(baseImg)
       }
     })
   }
   
   // 把image 转换为 canvas对象
   export function imgToCanvas (image) {
     var canvas = document.createElement('canvas')
     canvas.width = image.width
     canvas.height = image.height
     canvas.getContext('2d').drawImage(image, 0, 0)
     return canvas
   }
   

2. 将以上代码封装为一个js文件，这里命名为compressImg.js，放置在utils文件夹下
3. 在需要使用图片压缩的.vue文件中引入并使用，如下

   // 注意引入路径是否正确
   import { compressImgBySize } from '@/utils/compressImg'
   
   // this.applyFile[0].content 为指定的base64格式照片
   // 1200 指将图片压缩到1200kb大小以下
   compressImgBySize(this.applyFile[0].content, 1200).then(baseImg => {
   	console.log(baseImg)
   })