话不多说直接上代码

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
</head>

<body>
  <div id="app">
    <input type="file" accept="image/*" name="imageFile" @change="upload" />
    <img id="test" crossorigin="true" alt="">

  </div>
  <script>
    var app = new Vue({
      el: '#app',
      data() {
        return {
        }
      },
      components: {
      },
      created() {
      },
      methods: {
        upload() {
          let file = document.querySelector('input[type=file]').files[0] // 获取选择的文件，这里是图片类型
          let reader = new FileReader()
          reader.readAsDataURL(file) //读取文件并将文件以URL的形式保存在resulr属性中 base64格式
          reader.onload = (e) => { // 文件读取完成时触发
            let result = e.target.result // base64格式图片地址
            var image = new Image()
            image.src = result // 设置image的地址为base64的地址
            image.onload = () => { // 图片加载完成后才能进行压缩处理，从而转换为base64 进行赋值
              let width = image.width // 图片宽度
              let height = image.height
              let dataUrl = this.compress(image, width, height, 0.7)
              document.getElementById("test").src = dataUrl
            }
          }
        },
        /*
         * 图片压缩
         * img   原始图片
         * width  压缩后的宽度
         * height  压缩后的高度
         * ratio  压缩比率
        */
        compress(img, width, height, ratio) {
          let canvas, ctx, img64;
          canvas = document.createElement('canvas')
          canvas.width = width;
          canvas.height = height;
          ctx = canvas.getContext("2d");
          ctx.drawImage(img, 0, 0, width, height);
          img64 = canvas.toDataURL("image/jpeg", ratio);
          return img64;
        },
        //---------------------------------------------
        toFile(img64, type, name) {//img64：图片base64路径，type：图片类型，name：图片名
          // 转文件
          var arr = img64.split(","),
            bstr = atob(arr[1]),
            n = bstr.length,
            u8arr = new Uint8Array(n);
          while (n--) {
            u8arr[n] = bstr.charCodeAt(n);
          }
          return new File([u8arr], name, {
            type: type,
          });
        },
      }
    })
  </script>

  <style lang="less" scoped>
  </style>

</body>

</html>