图片预览 base64 element 图片上传 预览图

　　　　　　　　　　　　　　<el-upload
                          class="avatar-uploader" action="https://jsonplaceholder.typicode.com/posts/"
                          ref="upload"
                          :show-file-list="false"
                          :auto-upload="false"
                          :on-success="handleAvatarSuccess"
                          :before-upload="beforeAvatarUpload"
                          :on-change="onchange"
                          >
                          <img v-if="form.img" :src="form.img" class="avatar">
                          <i v-else class="el-icon-plus avatar-uploader-icon"></i>
                        </el-upload>
                        <el-button type="success" style="margin-left: 10px;" @click="upimg">上传</el-button>

onchange:function(file,filelist){
                let fileName = file.name;
                let regex = /(.jpg|.jpeg|.gif|.png|.bmp)$/;
                if (regex.test(fileName.toLowerCase())) {
                    // console.log(URL.createObjectURL(file.raw))
                    Vue.set(this.form,"img",URL.createObjectURL(file.raw))//新版本需要这么做,老版本好像file或者filelist里面直接就有url,使用Vue.set是应为需要重新渲染
                } else {
                    this.$message.error(‘请选择图片文件‘);
                }
            }

function img264(imgUrl){
                let that = this
                window.URL = window.URL || window.webkitURL;
                      var xhr = new XMLHttpRequest();
                      xhr.open("get", imgUrl, true);
                      // 至关重要
                      xhr.responseType = "blob";
                      xhr.onload = function () {
                        if (this.status == 200) {
                          //得到一个blob对象
                          var blob = this.response;
                          console.log("blob", blob)
                          // 至关重要
                          let oFileReader = new FileReader();
                          oFileReader.onloadend = function (e) {
                            let base64 = e.target.result;
                            console.log("方式一》》》》》》》》》", base64)
                            // that.form.img = base64
                            that.$set(form,"img",base64)
                          };
                          oFileReader.readAsDataURL(blob);
                          
                 
                        }
                      }
                      xhr.send();
            }