js下载图片

--imgName 下载照片的名称
--dataURI  base64
```javascript
var dataURIToBlob =  function (imgName, dataURI, callback) {
        var binStr = atob(dataURI.split(',')[1]),
            len = binStr.length,
            arr = new Uint8Array(len);

        for (var i = 0; i < len; i++) {
            arr[i] = binStr.charCodeAt(i);
        }

        callback(imgName, new Blob([arr]));
    }

    var callback = function (imgName, blob) {
        var triggerDownload = $("").attr("href", URL.createObjectURL(blob)).attr("download", imgName).appendTo("body").on("click", function () {
            if (navigator.msSaveBlob) {
                return navigator.msSaveBlob(blob, imgName);
            }
        });
        triggerDownload[0].click();
        triggerDownload.remove();
    };