compressor.js

结合Antd或者Element等Upload组件的BeforeUpload动作，对Blob数据进行处理，基于canvas，因此需要判断透明，非透明的直接转换为jpg，获取最优压缩比例；透明的直接压缩，输出前需要判断图片压缩大小，防止返回变大的图片

import Compressor from 'compressorjs'
async beforeUpload(file: Blob) {
    const curSize = file.size
    const dataURL = await filetoDataURL(file)
    const image = await dataURLtoImage(dataURL)
    const cvs = document.createElement('canvas')
    const ctx = cvs.getContext('2d')
    let isAlphaBackground = false
    if (ctx) {
      ctx.clearRect(0, 0, cvs.width, cvs.height)
      ctx.drawImage(image, 0, 0)
      const imageData = ctx.getImageData(0, 0, cvs.width, cvs.height).data
      // 检测有没有透明数据
      for (let index = 3; index < imageData.length; index += 4) {
        if (imageData[index] != 255) {
          isAlphaBackground = true
          break
        }
      }
    }
    if (this.compress) {
      return new Promise((resolve, reject) => {
        new Compressor(file, {
          quality: 0.9,
          convertSize: isAlphaBackground ? undefined : 1000,
          success(result) {
            console.log(result.size)
            const finalFile = result.size > file.size ? file : result
            resolve(finalFile)
          },
          error(error) {
            console.error(error)
            reject(error)
          }
        })
      })
    }
  }