JS图片上传

private getBase64(img: File, callback: (img: string) => void): void {
        const reader = new FileReader();
        reader.addEventListener('load', () => callback(reader.result!.toString()));
        reader.readAsDataURL(img);
    }

compressImg (file) {
        if (['image/png','image/jpeg','image/jpg'].includes(file.type)) {
            let _this = this;
            this.getBase64(file, (src) => {
                let img = new Image();
                img.src = src;
                img.onload = () => {
                    let originWidth = img.width;
                    let originHeight = img.height;
                    // 目标尺寸
                    let targetWidth = originWidth, targetHeight = originHeight;
                    let maxWidth =  'xxxx';
                    let maxHeight = 'xxx;
                    if (!maxWidth && !maxHeight) {
                        maxWidth = MAX_WIDTH;
                        maxHeight = MAX_HEIGHT;
                    }
                    if (originWidth > maxWidth || originHeight > maxHeight) {
                        if ((maxWidth && maxHeight) && (originWidth / originHeight > maxWidth / maxHeight) || maxWidth) {
                            targetWidth = maxWidth;
                            targetHeight = Math.round(maxWidth * (originHeight / originWidth));
                        } else {
                            targetHeight = maxHeight;
                            targetWidth = Math.round(maxHeight * (originWidth / originHeight));
                        }
                    }
                    // 新建画布
                    let canvas = document.createElement('canvas');
                    let context = canvas.getContext('2d');
                    canvas.width = targetWidth;
                    canvas.height = targetHeight;
                    // 清除画布
                    context.clearRect(0, 0, targetWidth, targetHeight);
                    // 图片压缩
                    context.drawImage(img, 0, 0, targetWidth, targetHeight);

                    canvas.toBlob((blob) => {
                        let formData = new FormData();
                        formData.append('file', blob, file.name);
                        //请求数据
                    })
                }
            });
        } else {
            console.log('error', '文件格式不正确');
        }
    }