vue element upload实现图片本地预览

<el-upload
 class="avatar-uploader"
 action="123" //这个路径不重要，可以随便写
 :show-file-list="false"
 :on-success="handleAvatarSuccess"
 :on-change="onchange"
 :before-upload="beforeAvatarUpload">
 <img v-if="imageUrl" :src="imageUrl" class="avatar">
 <i v-else class="el-icon-plus avatar-uploader-icon"></i>
</el-upload>

<script>
 export default {
  data() {
   return {
    imageUrl: '',
   };
  },
  methods: {
   handleAvatarSuccess(res, file) {
    this.imageUrl = URL.createObjectURL(file.raw);
   },
   beforeAvatarUpload(file) {
    const isJPG = file.type === 'image/jpeg';
    const isLt2M = file.size / 1024 / 1024 < 2;

    if (!isJPG) {
     this.$message.error('上传头像图片只能是 JPG 格式!');
    }
    if (!isLt2M) {
     this.$message.error('上传头像图片大小不能超过 2MB!');
    }
    return isJPG && isLt2M;
   },
   //当上传图片后，调用onchange方法，获取图片本地路径
   onchange(file,fileList){
     var _this = this;
        var event = event || window.event;
        var file = event.target.files[0];
        var reader = new FileReader(); 
        //转base64
        reader.onload = function(e) {
         _this.imageUrl = e.target.result //将图片路径赋值给src
        }
        reader.readAsDataURL(file);
   }
  }
 }
</script>