Downloader for binary files.

downloader.js

// Would be best to store this in ~/Scripts/durandal/plugins for convenience.
// This is so that when you must download a file from the web, via WebAPI with an OAuth2 token, you can validate yourself to the Api.
// This has been tested with small-ish files, but has not been tested with larger files, like installers.  Please offer contributions
// back for those items.
define(["durandal/system", "durandal/app"], function (system, app) {
    var defaults = {
        url: "", // to be provided by end user.
        method: "GET",
        mimeType: "application/octet-stream",
        filename: "download.bin",
        beforeSend: function (xhr) { }
    };

    return {
        beginDownload: function (parms) {

            var options = $.extend(defaults, parms);

            var url = options.url || "";

            if (url === "") {
                throw "Missing Url";
            }

            var xhr = new XMLHttpRequest();
            xhr.open(options.method, options.url, true);
            xhr.responseType = "blob";

            options.beforeSend(xhr);

            xhr.onreadystatechange = function () {
                /// Would like to build error capturing in this for error 400, 500, 401, 403, etc.
                if (!(xhr.readyState === 4 && xhr.status === 200)) {
                    return;
                }

                var success = false;
                var buffer = xhr.response;
                var filename = xhr.getResponseHeader("x-filename") || options.filename || "download.bin";
                var contentType = xhr.getResponseHeader("content-type") || options.mimeType;
                var blob = new Blob([buffer], { type: contentType });

                // Save Blob method.
                try {
                    system.log("Trying saveBlob method...");
                    system.log(filename);

                    var saveBlob = navigator.msSaveBlob || navigator.webkitSaveBlob || navigator.mozSaveBlob || navigator.saveBlob;

                    if (saveBlob === undefined) {
                        throw "Not Supported";
                    }
                    saveBlob(blob, filename);
                    system.log("saveBlob succeeded.");
                    success = true;
                } catch (ex) {
                    system.log("saveBlob method failed with the following exception:");
                    system.log(ex);
                }

                if (!success) {
                    var urlCreator = window.URL || window.webkitUrl || window.mozURL || window.msURL;
                    if (urlCreator) {
                        var link = document.createElement("a");
                        if ('download' in link) {
                            try {
                                system.log("Trying download link method with simulated click ...");
                                var url = urlCreator.createObjectURL(blob);

                                link.setAttribute("href", url);
                                link.setAttribute("download", filename);

                                var event = document.createEvent('MouseEvents');
                                event.initMouseEvent('click', true, true, window, 1, 0, 0, 0, 0, false, false, false, false, 0, null);
                                link.dispatchEvent(event);
                                console.log("Download link method with simulated click succeeded");
                                success = true;
                            } catch (ex) {
                                system.log("Download link method with simulated click failed with the following exception:");
                                system.log(ex);
                            }
                        }

                        if (!success) {
                            try {
                                system.log("Trying download link method with window.location ...");
                                var url = urlCreator.createObjectURL(blob);

                                window.location = url;
                                console.log("Download link method with window.location succeeded.")
                            } catch (ex) {
                                system.log("Download link method with window.location failed with the following exception:")
                                system.log(ex);
                            }
                        }
                    }
                }

                if (!success) {
                    system.log("No method worked for saving the arraybuffer.");
                }
            }

            xhr.send();
        }
    }
});