Front end: Convert base64 string to file through js and download the file

<!DOCTYPE html>
<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    <title></title>
    <meta charset="utf-8" />
</head>
<body>
    
    <script>
		/**封装blob对象*/
        function dataURLtoBlob(base64Str, mimeTypeStr) {
			var bstr = atob(base64Str), n = bstr.length, u8arr = new Uint8Array(n);
			while (n--) {
				u8arr[n] = bstr.charCodeAt(n);
			}
			return new Blob([u8arr], { type: mimeTypeStr });
		}
		/**创建一个a标签，并做下载点击事件*/
		function downloadFile(hrefUrl,fileName){
			var a = document.createElement("a")
			a.setAttribute("href",hrefUrl)
			a.setAttribute("download",fileName)
			a.setAttribute("target","_blank")
			let clickEvent = document.createEvent("MouseEvents");
			clickEvent.initEvent("click", true, true);  
			a.dispatchEvent(clickEvent);
			
			
		}
		/**下载文件的方法*/
		function downloadFileByBase64(base64Str, mimeTypeStr, fileName){
			var myBlob = dataURLtoBlob(base64Str, mimeTypeStr)
			var myUrl = URL.createObjectURL(myBlob)
			downloadFile(myUrl,fileName)
		}






/*************************** 测试代码 start ************************/
		
		var tupian='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';
		
		downloadFileByBase64(tupian, 'image/png', 'tupian.png');

		/*************************** 测试代码 end ************************/

    </script>
</body>
</html>
Front end: Convert base64 string to file through js and download the file

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