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How to download data to a client in AngularDart?

How can I provide the user of a web-app with a download-link to programmatically created data in AngularDart?
I thought this would be an easy task, since the download of data could be handled via data-links. But it turns out that AngluarDart doesn't let me use data-links since they are considered unsecure. In a pure Javascript environment I would use Filesaver.js, but also this is not possible with AngularDart (at least I didn't find a way to use it there).
What I really want to do: I create data in the app with code. At the end i have a json-structure that needs to be downloaded to the client computer of the user. He should be presented with a file select dialog where he can enter a filename and then the data should be saved there. And this should be initiated by a click on a button.
Up to now i didn't find a working way to make this happen in AngularDart. I tried BrowserClient, a-tags with download attribute, forms with data-url, but nothing works.
If anybody could give me a hint how to make this work, I would be very happy. A hint on how to use Javascript-Libraries (like FileSaver.js) in AngularDart would also be welcome.
I don't use Flutter and also I need this to work in the browser. So File from dart:io is no solution for me (this will be one of the first things you find, when searching for a solution). Also it is no solution to save the file to the server and download it to the client.

Cordova - Saving/ Downloading a backup JSON file that is dynamically generated

I am building an HTML5 phonegap application. This app exports data so that the user can backup and restore any time. I'm doing this exporting with the following javascript code:
var dataStr = "data:text/json;charset=utf-8," + encodeURIComponent(JSON.stringify(this.data, null, "\t"));
var dlAnchorElem = document.createElement('a');
dlAnchorElem.setAttribute("href", dataStr);
dlAnchorElem.setAttribute("download", "data.json");
document.body.appendChild(dlAnchorElem);
dlAnchorElem.click();
This generates an anchor tag with an encoded file and clicks so it downloads. Works great on browser, but does nothing in a compiled Cordova application.
After doing some research, I found that the default solution would be to use a download plugin for Cordova, specifically this one: https://github.com/apache/cordova-plugin-file-transfer
I read the documentation, but it does not seem to take an encoded file as parameter, but an encoded URL for download. Also, it takes the save path on the phone, which I prefer would just default to the download folder.
My question is: What is the best way to achieve this, considering I'm dynamically generating the JSON backup file. Is there perhaps an AndroidManifest directive that allows for file downloads?

After some research and trying many different hacks, I came to the conclusion that it's currently not allowed natively with cordova or with the available plugins. My solution was to, instead of writing to the filesystem, use the web share api to let the user export the way he finds best (including file, if he chooses dropbox, onedrive or google drive).

Sitecore Pipeline Upload Processor

I'm using UploadProcessor to block specific file uploading into MediaLibrary.
Everything is working good and I can see the alert Sitecore's message. But, Sitecore's error message is not really user-friendly "One or more files could not be uploaded. See the Log file for more details"
So, I'd like to add extra alert box for users. Below is my code, but the javascript is not working.
Some people want me to use "SheerResponse", but Sitecore Document mentions that
The uiUpload pipeline is run not as part of the Sheer event, but as part of the form loading process in response to a post back. This is because the uploaded files are only available during the “real” post back, and not during a Sheer UI event. In this sense, the uiUpload pipeline has not been designed to provide UI. In order to provide feedback to a User, the processor should resort to some trick which emits the JScript code.
http://sdn.sitecore.net/Articles/Media/Prevent%20Files%20from%20Uploading/Pipeline%20upload.aspx
Do you have any idea how to implement alert box??

The Upload control in the Media Library uses flash to upload the files. As part of this upload process, the file sizes are checked using JavaScript and a client side validation is made before the upload.
There are a number of changes you need to make. I'm just going to list them here, you can find all the code in my Github Gists:
https://gist.github.com/jammykam/54d6af46593fa3b827b4
1) Extend and update the MediaFolder.js file to check the file size against the Image Size ONLY if the extension is one specified in config
if (file.size > this.uploadLimit() || this.uploadImageLimitReached(file)) {
...
}
2) Update MediaFolder.xml page to include the above JS. Amend the codebeside, inheriting from Sitecore.Shell.Applications.Media.MediaFolder.MediaFolderForm and overriding OnLoad and OnFilesCancelled, to render restricted extensions and max image size settings so these are passed to the Javascript and display friendly alert.
settings.Add("uploadImageLimit", ((long)System.Math.Min(ImageSettings.MaxImageSizeInDatabase, Settings.Runtime.EffectiveMaxRequestLengthBytes)).ToString());
settings.Add("uploadImageRestrictedExtensions", ImageSettings.RestrictedImageExtensions);
3) Update Attach.xaml.xml codebeside to check image size, inheriting from Sitecore.Shell.Applications.FlashUpload.Attach.AttachPage and overriding OnQueued method:
if (ImageSettings.IsRestrictedExtension(filename) && num > maximumImageUploadSize)
{
string text = Translate.Text("The image \"{0}\" is too big to be uploaded.\n\nThe maximum image size that can be uploaded is {1}.", new object[] { filename, MainUtil.FormatSize(maximumImageUploadSize) });
this.WarningMessage = text;
SheerResponse.Alert(text, new string[0]);
}
else
{
base.OnQueued(filename, lengthString);
}
4) Add a config include with the new settings.
<setting name="Media.MaxImageSizeInDatabase" value="1MB" />
<setting name="Media.RestrictedImageExtensions" value=".jpg|.jpeg|.png|.gif|.bmp|.tiff" />
You can still (and should) keep the pipelines in place, but note from my previous answer I gave the "Restricted Extension" config setting has now changed (into a single setting instead of passing it into the pipeline). The Gist contains the
NOTE that I have tested this using Sitecore 7.2 rev 140526, so the base code is taken from there. If you are using a different version then you should check the base C#, JS and XML code matches what I have provided. The code is commented to show you what has changed.
The above works in the Content Editor, it does not work in the Page Editor! Which in Sitecore 7.2+ uses SPEAK dialogs and it looks like they use a different set of pipelines. That would need more investigation (raise another question, and specify which version of Sitecore you are using).

Writing a custom file format downloader in Google Spreadsheets

What I'm aiming to do is write something akin to the File > Download as > * functionality currently in Google Spreadsheets, but I want it to be in a custom format.
Specifically, I want to turn a spreadsheet of financial transactions into an QIF or OFX file for importing into accounting software. In essence, pushing a button on the UI will download a QIF/OFX version of the currently open spreadsheet.
I have tried the following so far:
Publishing a service (via implementing doGet) that uses ContentService to create the custom file and return it as a download using TextOutput.downloadAsFile(). This works if I call the endpoint directly using my browser.
Tried redirecting the browser to the Service's URL via window.location, but that doesn't seem to be available in the context of the App Script.
Tried using UrlFetchApp.fetch to have the front-end (the spreadsheet) have the browser navigate to the URL for the service. This didn't work either (not really surprising).
So, is this the right approach here? How else can I attack this?

Looks like this is what you have to do.
Create a UiApp
Add a link to the download inside that app.
Show the UiInstance on the spreadsheet
It's a little bit bulky, but it seems the be the cleanest solution.
function downloadAsWhatever() {
var app = UiApp.createApplication();
app.add(app.createAnchor("Download the file now!", "https://script.google.com/macros/s/[...]/exec"))
SpreadsheetApp.getActiveSpreadsheet().show(app.setWidth(300).setHeight(150));
}
You can set the size of the app to whatever you'd like. I chose to set it smaller so it takes up less space on the Spreadsheet screen.
For now the best way to direct a user to a new page is to create an anchor widget and have them click it. We understand that this is not an ideal user experience, but it should suffice for must use cases.
Source

Get binary image data from input type "file" using JavaScript/jQuery for use with picture preview with AJAX in WebMatrix [duplicate]

This question already has answers here:
Closed 10 years ago.
I have had trouble when researching or otherwise trying to figure out how (if it's even possible) to get binary image data using JavaScript/jQuery from an html input element of type file.
I'm using WebMatrix (C#), but it may not be necessary to know that, if the purposes of this question can be answered using JavaScript/jQuery alone.
I can take the image, save it in the database (as binary data), then later show the pic on the page, from the binary data, after posting. This does, however, leave me without a pic preview, before uploading, for which I am almost certain I must use AJAX.
Again, this may not even be possible, but as long as I can get the binary image data, I believe I can push it to the server with AJAX and process the image the same way I would if I were taking it from a database (note that I don't save the image files themselves using GUID and all that,I just save the binary data).
If there is an easier way to show a pic preview using the input element, that would work fine, too, of course, as the whole idea behind me trying to do this is to show a pic preview before they hit the submit form button (or at least create that illusion).
**********UPDATE***********
I do not consider this a duplicate of another question because, my real question is:
How can I get image data from an input type "file", with JavaScript/jQuery?
If I can just get the data (in the right format) back to the server, I should be able to work with it there, and then return it with AJAX (although, I am absolutely no AJAX expert).
There is, according to the research that I have done, NO WAY to get picture previews in all IE versions using only javascript (this is because getting the full file path is seen, by them, as a potential security risk). I could ask my users to add the site to the trusted sites, but you don't usually ask users to tamper with those kinds of settings (not to mention the quickest way to make your site seem suspicious to users is to ask them to directly add your site to the trusted sites list. That's like sending an email and asking for a password. "Just trust me! I'm soooo safe!" :)

Short answer: Use the jQuery form plugin, it suports AJAX-like form submits even for file uploads.
tl;dr
Thumbnail preview is popular websites is usually done by a number of steps, basically the website do these steps:
upload the RAW image
Resize and optimise the image for data storage
Generate a temporary link to that file (usually stored in a server maintained HTTP session)
Send it back to the user, to enable a 'preview'
Actually store the image after user confirms the image
A few bad solutions are:
Most of the modern browsers has options to enable script access to local files, but usually you don't ask your users to tinker with those low level settings.
Earlier Internet Explorer (ah... yes it's a shame) and ancient versions of modern browsers will expose the full file path by reading the 'value' of file input box, which you can directly generates an tag and use that value. (Now it is replaced by some c:/fakepath/... thing.)
Use Adobe Flash to mimic the file selection panel, it can properly read local files. But passing it into JavaScript is another topic...
Hope these helps. ;)
UPDATE
I actually came across a situation that requires a preview before uploading, I'd like to also put it here. As I could recall, there were no transitional versions in modern browsers that do not implement FileReader before masking the real file path, but feel free to correct me if so. This solution should caters most of the browsers, as long as they are supported by jQuery.
// 1. Listen to change event
$(':file').change(function() {
// 2. Check if it has the FileReader class
if (!this.files) {
// 2.1. Old enough to assume a real path
setPreview(this.value);
}
else {
// 2.2. Read the file content.
var reader = new FileReader();
reader.onload = function() {
setPreview(reader.result);
};
reader.readAsDataURL();
}
});
function setPreview(url) {
// Do preview things.
$('.preview').attr('src', url);
}