elementui上传图片功能(vue)

            //文件上传
            fileUpload(e){
                let vm=this;
                if (e.target.files.length==0){
                    return false;
                }
                if(e.target.files[0].type!=='image/jpeg'&&e.target.files[0].type!=='image/png'){
                    this.$message.error('上传图片只能是JPG/PNG格式!');
                    return false
                }
                if (e.target.files[0].size/1024/1024>5){
                    this.$message.error('上传图片大小不超过5M');
                    return false
                }
                let option={file:e.target.files[0]}
                var reader = new FileReader();
                //files[0]对象是从input type=file中获取的file对象
                reader.readAsDataURL(option.file);
                //将file对象base64转码成功后进入
                reader.onload = function () {
                    //声明img标签，并将未压缩的图片赋值给src属性
                    var image = document.createElement('img')
                    image.setAttribute('src', this.result);
                    image.addEventListener('load', function () {
                        var canvas = document.createElement('canvas');
                        var context = canvas.getContext('2d');
                        var originWidth = this.width;
                        var originHeight = this.height;
                        // 最大尺寸限制
                        var maxWidth = 1500
                        // 目标尺寸
                        var targetWidth = originWidth, targetHeight = originHeight;
                        // 图片尺寸超过宽度400的限制
                        if (originWidth > maxWidth) {
                            // 更宽，按照宽度限定尺寸
                            targetWidth = maxWidth;
                            targetHeight = Math.round(maxWidth * (originHeight / originWidth));
                        }
                        // canvas对图片进行缩放
                        canvas.width = targetWidth;
                        canvas.height = targetHeight;
                        context.drawImage(this, 0, 0, targetWidth, targetHeight);
                        var dataBase = canvas.toDataURL(e.target.files[0].type);
                        // 将base64转换为files对象
                        var arr = dataBase.split(','),
                            mime = arr[0].match(/:(.*?);/)[1],
                            bstr = atob(arr[1]),
                            n = bstr.length,
                            u8arr = new Uint8Array(n);
                        while(n--){
                            u8arr[n] = bstr.charCodeAt(n);
                        }
                        let file=new File([u8arr], e.target.files[0].type=='image/jpeg'?'img.jpg':'img.png', {type:mime});
                        // 将files对象压缩为二进制
                        let formData = new FormData();
                        formData.append( 'file'  , file );
                        //ajax请求
                        vm.$api.upload.upload(( flag, result )=>{
                            if( flag ){
                                vm.form.Pic=result.data.Data.URL
                            }
                        }, formData );
                    });
                };
            }