sample.js

DrawingBoard.Board.prototype.downloadImg = function () {
    var canvas = $("canvas").get(0);
    var base64 = canvas.toDataURL();
    var blob = Base64toBlob(base64);
    saveBlob(blob, "pronama-chan-tshirt.png");
};

function Base64toBlob(_base64) {
    var i;
    var tmp = _base64.split(',');
    var data = atob(tmp[1]);
    var mime = tmp[0].split(':')[1].split(';')[0];
    var arr = new Uint8Array(data.length);
    for (i = 0; i < data.length; i++) { arr[i] = data.charCodeAt(i); }
    var blob = new Blob([arr], { type: mime });
    return blob;
}
function saveBlob(_blob, _file) {
    if ( /*@cc_on ! @*/ false) {
        window.navigator.msSaveBlob(_blob, _file);
    }
    else {
        var url = (window.URL || window.webkitURL);
        var data = url.createObjectURL(_blob);
        var e = document.createEvent("MouseEvents");
        e.initMouseEvent("click", true, false, window, 0, 0, 0, 0, 0, false, false, false, false, 0, null);
        var a = document.createElementNS("http://www.w3.org/1999/xhtml", "a");
        a.href = data;
        a.download = _file;
        a.dispatchEvent(e);
    }
}