话不多,看代码!

1、将图片的url转换成base64

urlTobase64(url) {
  var that = this
  var img = new Image()
  img.src = url + '?time=' + new Date().valueOf() // 加上时间结尾,处理缓存
  
   //支持http跨域图片。需要后端设置图片支持跨域为*(如果后端不处理,加上这行会无法显示图片,导致拿不到base64)
  img.setAttribute('crossOrigin', '*') 
  if (url) {
    img.onload = function() {
      var base64Url = that.getBase64Image(img)
      console.log(base64Url) // 最终拿到的base64值
    }
  }
},
getBase64Image(img) {
  var canvas = document.createElement('canvas')
  canvas.width = img.width
  canvas.height = img.height
  var ctx = canvas.getContext('2d')
  ctx.drawImage(img, 0, 0, img.width, img.height)
  const dataURL = canvas.toDataURL('image/jpeg') // 可根据图片后缀,动态变换如 image/png
  return dataURL
},

2、将图片的file类型转换成base64,压缩图片大小

html:

<el-upload
  class="up-btn"
  action=""
  list-type="picture-card"
  :multiple="false"
  :show-file-list="false"
  :before-upload="beforeAvatarUpload">
  <i class="el-icon-plus"></i>
</el-upload>

js:

// 上传图片
beforeAvatarUpload(file) {
 // 判断扩展名
 const tmpcnt = file.name.lastIndexOf('.')
 const exname = file.name.substring(tmpcnt + 1)
 const names = ['jpg', 'jpeg', 'png']
 if (names.indexOf(exname) < 0) {
   this.$message.error('不支持的格式!')
   return
 }
 if (file.size > 1024 * 1024 * 5) {
   this.$message.error('图片大小最大5M')
   return
 }
 this.urlTobase64(file)
},
// 图片转base64
urlTobase64(file) {
 var that = this
 var reader = new FileReader()
 reader.readAsDataURL(file)
 reader.onload = function(e) { // 读取完毕后调用接口
 // 获取到base64值
 var img64 = e.target.result
 // 图片大于1M的时候执行压缩
  if (img64.length > 1024 * 1024 * 1) {
    var size = (1024 * 1024 * 1) / img64.length
    that.compress(file, img64, size) // size越小压缩效果越大
  }
 }
},
// 压缩图片
compress(file, img64, size) {
 var that = this
 var img = document.getElementById('base64Url')
 var width, height
 // 加载完成执行
 img.onload = function() { // base64地址图片加载完毕后执行
   width = img.width
   height = img.height
   var canvas = document.createElement('canvas')
   var ctx = canvas.getContext('2d')
   // var initSize = img.src.length
   canvas.width = width
   canvas.height = height
   // 铺底色
   ctx.fillStyle = '#fff'
   ctx.fillRect(0, 0, canvas.width, canvas.height)
   ctx.drawImage(img, 0, 0, width, height)
   // 进行最小压缩后的base64
   var base64Url = canvas.toDataURL('image/jpeg', size)
   console.log(base64Url)
 }
}
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