下载图片到本地

/**
 * 下载图片类
 */
export class DownloadImg {
   /**
    * 下载图片
    * @param url
    */
   public static downloadImg(url: string) {
      this.convertUrlToBase64(url).then(res => {
         // 图片转为base64
         const blob = this.convertBase64UrlToBlob(res); // 转为blob对象
         // 下载
         if (this.myBrowser() == 'IE') {
            window.navigator.msSaveBlob(blob, name + '.jpg');
         } else if (this.myBrowser() == 'FF') {
            window.location.href = url;
         } else {
            const a = document.createElement('a');
            a.download = name;
            a.href = URL.createObjectURL(blob);
            a.click();
         }
      });
   }

   /**
    * base64转换
    * @param url
    * @private
    */
   private static async convertUrlToBase64(url: any) {
      return new Promise(function(resolve) {
         const img = new Image();
         img.crossOrigin = 'Anonymous';
         img.src = url;
         img.onload = function() {
            const canvas = document.createElement('canvas');
            canvas.width = img.width;
            canvas.height = img.height;
            const ctx = canvas.getContext('2d');
            ctx?.drawImage(img, 0, 0, img.width, img.height);
            const ext = img.src.substring(img.src.lastIndexOf('.') + 1).toLowerCase();
            const dataURL = canvas.toDataURL('image/' + ext);
            const base64 = {
               dataURL: dataURL,
               type: 'image/' + ext,
               ext: ext,
            };
            resolve(base64);
         };
      });
   }

   /**
    * 加工blob对象
    * @param base64
    * @private
    */
   private static convertBase64UrlToBlob(base64: any) {
      const parts = base64.dataURL.split(';base64,');
      const contentType = parts[0].split(':')[1];
      const raw = window.atob(parts[1]);
      const rawLength = raw.length;
      const uInt8Array = new Uint8Array(rawLength);
      for (let i = 0; i < rawLength; i++) {
         uInt8Array[i] = raw.charCodeAt(i);
      }
      return new Blob([uInt8Array], { type: contentType });
   }

   /**
    * 浏览器判断
    */
   public static myBrowser() {
      const userAgent = navigator.userAgent; //取得浏览器的userAgent字符串
      if (userAgent.indexOf('OPR') > -1) {
         return 'Opera';
      } //判断是否Opera浏览器 OPR/43.0.2442.991
      if (userAgent.indexOf('Firefox') > -1) {
         return 'FF';
      } //判断是否Firefox浏览器  Firefox/51.0
      if (userAgent.indexOf('Trident') > -1) {
         return 'IE';
      } //判断是否IE浏览器  Trident/7.0; rv:11.0
      if (userAgent.indexOf('Edge') > -1) {
         return 'Edge';
      } //判断是否Edge浏览器  Edge/14.14393
      if (userAgent.indexOf('Chrome') > -1) {
         return 'Chrome';
      } // Chrome/56.0.2924.87
      if (userAgent.indexOf('Safari') > -1) {
         return 'Safari';
      } //判断是否Safari浏览器 AppleWebKit/534.57.2 Version/5.1.7 Safari/534.57.2
   }
}