js把base64转为可下载文件

1、html代码放一个a标签

<a href=""></a>

2、js代码

	var downLoad =  document.querySelectorAll('#down a')[0];

	var downLoad =  document.querySelectorAll('#down a')[0];
        var blob = getBlob(base64Text);
		                   downLoad.setAttribute('href',URL.createObjectURL(blob));
        function getBlob(base64) {
        	console.log(getContentType(base64))
            return b64toBlob(getData(base64), getContentType(base64));
        }          
        function getContentType(base64) {
            return /data:([^;]*);/i.exec(base64)[1];
        }
 
        function getData(base64) {
            return base64.substr(base64.indexOf("base64,") + 7, base64.length);
        }
        
        function b64toBlob(b64Data, contentType, sliceSize) {
            contentType = contentType || '';
            sliceSize = sliceSize || 512;
 
            var byteCharacters = atob(b64Data);
            var byteArrays = [];
 
            for (var offset = 0; offset < byteCharacters.length; offset += sliceSize) {
                var slice = byteCharacters.slice(offset, offset + sliceSize);
 
                var byteNumbers = new Array(slice.length);
                for (var i = 0; i < slice.length; i++) {
                    byteNumbers[i] = slice.charCodeAt(i);
                }
 
                var byteArray = new Uint8Array(byteNumbers);
 
                byteArrays.push(byteArray);
            }
 
            var blob = new Blob(byteArrays, { type: contentType });
            return blob;
        }