el-upload手动上传图片,限制图片大小、格式

部分代码：

template部分

<!-- 修改弹窗 -->
   <el-dialog :title="dialogTxt"
              @close="closeDialog"
              :visible.sync="alertBox"
              >
              <el-form
                   ref="addForm"
                   :rules="rules"
                  :model="addForm"
                  size="medium"
                  label-width="100px">
              <el-row>
                <el-col :span="12">
                <el-form-item label="知识标题：" prop="knowledgeTitle">
                  <el-input v-model="addForm.knowledgeTitle" ></el-input>
                </el-form-item>
                </el-col>
                <el-col :span="12">
                <el-form-item label="内容：" prop="knowledgeContent">
                  <el-input v-model="addForm.knowledgeContent"></el-input>
                </el-form-item>
                </el-col>


<!-- 图片上传 -->
                <el-col :span="12">
                <el-form-item label="图片选择：" >
                <el-upload
                  action="#"
                  ref="uploadimg"
                  :limit="1"
                  :auto-upload="false"
                  :on-change="imageChange"
                  :show-file-list="true"
                  :http-request="httpRequest"
                  :file-list="fileList"
                  list-type="picture-card"
                  :on-exceed="handleExceed"
                  :before-remove="handleRemove"
                  >
                  <i class="el-icon-plus"></i>
                </el-upload>
                </el-form-item>
                </el-col>
                <el-col :span="12">
                  <el-form-item label="状态：" prop="knowledgeStatus">
                    <el-select
                    v-model="addForm.knowledgeStatus"
                    placeholder="请选择"
                    @change="selectStatus"
                    >
                      <el-option label="可用" value='0'>
                      </el-option>
                      <el-option label="已禁止" value='1'>
                      </el-option>
                    </el-select>
                  </el-form-item>
                </el-col>
            </el-row>
            <el-row>
              <div class="submitBtn">
                <el-button type="primary" icon="el-icon-check"
                @click="uploadSucess('addForm')"
                >提交</el-button>
                <el-button type="danger" icon="el-icon-circle-close"
                @click="cancleUpload"
                >取消</el-button>
              </div>
            </el-row>
        </el-form>
    </el-dialog>

methods:

//关闭弹框清空校验信息
     closeDialog(){
       this.$refs.expertForm.clearValidate();
     },
     //选择图片后做图片格式限制（手动上传图片时，before-upload钩子无效，使用此方法替代）
     imageChange(file, fileList) {
       const isImage = file.raw.type == 'image/png' || file.raw.type == 'image/jpg' ||  file.raw.type == 'image/jpeg';
       const isLt5M = file.size <  1024 * 1024 * 5;
       if (!isImage) {
         this.$message.error('上传只能是png,jpg,jpeg格式!');
       }
       if (!isLt5M) {
         this.$message.error('上传图片大小不能超过 5MB!');
       }

       if(isImage && isLt5M){
         this.uploadFile =  file.raw || null;
       }else{
         fileList.splice(-1,1);
       }
     },


     //超出限制个数钩子
    handleExceed(files) {
      this.$message.warning('当前限制选择1个文件');
    },
    // 删除图片
    handleRemove(file,fileList) {
      console.log(file);
      fileList.splice(0,1);
      this.fileList=fileList;
      this.uploadFile = null;
      console.log('3333333',this.fileList);
      this.changeUrl = file.url;
    },


    httpRequest(params){
      //解决删除文件时报错
      const prom = new Promise((resolve, reject) => {})
      prom.abort = () => {}
      return prom
    },
    selectStatus(){
      this.ifStatus = true;
    },
    //  上传提交
     uploadSucess(formName){
         this.$refs.uploadimg.submit();
         let formData = new FormData();
       if(this.addText=="add"){
         if(!this.uploadFile){
           this.$message.error('图片不能为空！')
         }else{
           formData.append("file",this.uploadFile);
           formData.append("title",this.addForm.knowledgeTitle);
           formData.append("content",this.addForm.knowledgeContent);
           formData.append("status",this.addForm.knowledgeStatus);
           this.$refs[formName].validate((valid)=>{
             if(valid){
               this.$store.dispatch("baseSet/uploadSucess",formData)
                 .then(()=>{
                   this.knowledgeManager(this.pageNum);
                   this.alertBox = false;
                   this.$refs.uploadimg.clearFiles();
                   this.ifStatus = false;
                 })
             }
           })
         }

       }else{
         if(!this.uploadFile){
           this.$message.error('图片不能为空！')
         }else{
           if(this.uploadFile){
             formData.append("file",this.uploadFile);
           };

           formData.append("title",this.addForm.knowledgeTitle);
           formData.append("content",this.addForm.knowledgeContent);
           formData.append("status",this.addForm.knowledgeStatus);
           formData.append("id",this.changeId);
           this.$refs[formName].validate((valid)=>{
             if(valid){
               this.$store.dispatch("baseSet/changeKnowledge",formData)
                 .then(()=>{
                   this.knowledgeManager(this.pageNum);
                   this.alertBox = false;
                   this.$refs.uploadimg.clearFiles();
                   this.ifStatus = false;
                 })
             }
           })
         }
       }
     },
     cancleUpload(){
       this.alertBox = false;
       this.fileList = [];
     },