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How to store and load/display local PDFs with browser-data, from a website

I'm working with an extremely old database system containing people and associated PDFs. I can access most data over a webbrowser, however PDFs cannot be requested via web-api - I do however have the liberty of loading any javascript library, and use chrome webdev console.
I want to get a proof of principle working, where I can load a person's PDFs. But I'm not quite sure what the best approach is.
Idea to upload a file to the website's local storage in my browser (since it's viewed several times). However I seem to be lacking a good library to save/load files from the cache directory. This library wasn't updated since 2016 and Filesaver.js doens't seem to be keen on loading the files after saving. Using a fully-fledged database implementation seems overkill (most files will be <= 5-10MB)
Loading a file from local storage (even if dir is added to workspace in chrome) seems completely impossible, that would've been an alternative
adding the local file path to a <a href=""> element did not work in chrome
Is there a feasible approach to manage/associate PDF files on my local drive with the website I'm working with (and have full client-side control, i.e. can load any library)?
Note: Access is restricted, no chrome addons can be used and chrome cannot be started using custom flags

I don't exactly know what you are asking for, but this code will get all the pdfs in a selected directory and display them and also makes a list of all the file objects. This will only work in a "secure context" and on chrome
(it also wont run in a sandbox like a stackoverflow code snippet)
js
let files = [];
async function r() {
for await (const [_, h] of (await window.showDirectoryPicker()).entries()) files.push(await h.getFile());
files = files.filter(f => f.type === "application/pdf");
for (const f of files) {
let e = document.createElement("embed");
e.src = URL.createObjectURL(f), e.type = f.type;
document.body.appendChild(e);
}
}
html
<button onclick="r()">read PDFs</button>
also you can probably use this if you need to send the local PDF somewhere
not sure this answers the question but i hope it helps

Since ActiveX controls are no longer available browsers can display a PDF or a user can download the pdf.
For any more control over that I suspect you could try render the pdf using a JavaScript library like https://mozilla.github.io/pdf.js/
For full control you wont be in a position to control the PDF version, you could alternatively render the PDFs to images on the server and display image versions of the pages.

Browser hangs on reading large folder on client side

I am trying to create a simple folder uploader (client side). The minimum required functionality is to be able to select a folder/file(s) and show on the browser the information of all files. I have used a simple input element:
const ReadFolder = () => {
const onFileChange = (event: React.ChangeEvent<HTMLInputElement>) => console.log(event.target.files);
return (
<input
type='file'
directory
webkitdirectory
multiple
onChange={onFileChange}
/>
);
}
The onFileChange function just shows the info of received file list.
It works fine for small folders, but when I try to upload a git repository from my computer (which has a large nested folder hierarchy), the browser window becomes unresponsive for around 2 minutes before the onChange event is reported. Is there a way I can avoid this unresponsiveness? Can I push this processing to background (or to a web worker)?

This processing may not even be done by the browser's process, but rather by the OS directly, which is building a list of metadata for all the files in the directory and its sub-directories. That is a lot of I/O.
You are not the first one to report such an issue with some configurations (OS or file system, it's still unclear to me) having trouble to generate files' metadata when being asked by the browser through the <input type="file">.
So moving whatever to a Worker would most probably not help at all. My educated guess would be that your HDD is the bottleneck, not the CPU.
What you can try in supporting browsers, is to request a handle over the directory rather than requesting all the files in a single call.
The new File System API has a showDirectoryPicker method which would allow you to gain access to the directory, and to read only the files you need, and if you need them all, to do this in a streaming manner, allowing your page to render part of what has already been parsed while it is being parsed.
You can see a live demo here, which will currently only work in Chrome.
Note that directories gotten from a drag&drop event should not be read entirely either, and that you should also be able to navigate them by batches, with better browser support, so if you can, try to make your UI force your users to use this method instead.

Is it possible to download an html file from a given webpage using my local network/browser as if I downloaded it myself with javascript or nodejs?

I’m a bit new to javascriipt/nodejs and its packages. Is it possible to download a file using my local browser or network? Whenever I look up scraping html files or downloading them, it is always done through a separate package and their server doing a request to a given url. How do I make my own computer download a html file as if I did right click save as on a google chrome webpage without running into any server/security issues and errors with javascript?

Fetching a document over HTTP(S) in Node is definitely possible, although not as simple as some other languages. Here's the basic structure:
const https = require(`https`); // use http if it's an http url;
https.get(URLString, res => {
const buffers = [];
res.on(`data`, data => buffers.push(data));
res.on(`end`, ()=>{
const data = Buffer.concat(buffers);
/*
from here you can do what you want with the data. You can write it to a file
with fs, you can console.log it using data.toString(), etc.
*/
});
})
Edit: I think I missed the main question you had, give me a sec to add that.
Edit 2: If you're comfortable with doing the above, the way you access a website the same way as your browser is to open up the developer tools (F12 on Chrome) go to the network tab, find the request that the browser has made, and then using http(s).get(url, options, callback), set the exact same headers in the options that you see in your browser. Most of the time you won't need all of them, all you'll need is the authentication/session cookie.

How to Launch a PDF from a UWP (Universal Windows Platform) Web Application

I've converted an existing web application (HTML5, JS, CSS, etc.) into a Windows UWP app so that (hopefully) I can distribute it via the Windows Store to Surface Hubs so it can run offline. Everything is working fine, except PDF viewing. If I open a PDF in a new window, the Edge-based browser window simply crashes. If I open an IFRAME and load PDFJS into it, that also crashes. What I'd really like to do is just hand off the PDF to the operating system so the user can view it in whatever PDF viewer they have installed.
I've found some windows-specific Javascript APIs that seem promising, but I cannot get them to work. For example:
Windows.System.Launcher.launchUriAsync(
new Windows.Foundation.Uri(
"file:///"+
Windows.ApplicationModel.Package.current.installedLocation.path
.replace(/\//g,"/")+"/app/"+url)).then(function(success) {
if (!success) {
That generates a file:// URL that I can copy into Edge and it shows the PDF, so I know the URL stuff is right. However, in the application it does nothing.
If I pass an https:// URL into that launchUriAsync function, that works. So it appears that function just doesn't like file:// URLs.
I also tried this:
Windows.ApplicationModel.Package.current.installedLocation.getFileAsync(url).then(
function(file) { Windows.System.Launcher.launchFileAsync(file) })
That didn't work either. Again, no error. It just didn't do anything.
Any ideas of other things I could try?
-- Update --
See the accepted answer. Here is the code I ended up using. (Note that all my files are in a subfolder called "app"):
if (location.href.match(/^ms-appx:/)) {
url = url.replace(/\?.+/, "");
Windows.ApplicationModel.Package.current.installedLocation.getFileAsync(("app/" + url).replace(/\//g,"\\")).then(
function (file) {
var fn = performance.now()+url.replace(/^.+\./, ".");
file.copyAsync(Windows.Storage.ApplicationData.current.temporaryFolder,
fn).then(
function (file2) {
Windows.System.Launcher.launchFileAsync(file2)
})
});
return;
}
Turns out you have to turn the / into \ or it won't find the file. And copyAsync refuses to overwrite, so I just use performance.now to ensure I always use a new file name. (In my application, the source file names of the PDFs are auto-generated anyway.) If you wanted to keep the filename, you'd have to add a bunch of code to check whether it's already there, etc.

LaunchFileAsync is the right API to use here. You can't launch a file directly from the install directory because it is protected. You need to copy it first to a location that is accessible for the other app (e.g. your PDF viewer). Use StorageFile.CopyAsync to make a copy in the desired location.
Official SDK sample: https://github.com/Microsoft/Windows-universal-samples/tree/master/Samples/AssociationLaunching

I just thought I'd add a variation on this answer, which combines some details from above with this info about saving a blob as a file in a JavaScript app. My case is that I have a BLOB that represents the data for an epub file, and because of the UWP content security policy, it's not possible simply to force a click on a URL created from the BLOB (that "simple" method is explicitly blocked in UWP, even though it works in Edge). Here is the code that worked for me:
// Copy BLOB to downloads folder and launch from there in Edge
// First create an empty file in the folder
Windows.Storage.DownloadsFolder.createFileAsync(filename,
Windows.Storage.CreationCollisionOption.generateUniqueName).then(
function (file) {
// Open the returned dummy file in order to copy the data to it
file.openAsync(Windows.Storage.FileAccessMode.readWrite).then(function (output) {
// Get the InputStream stream from the blob object
var input = blob.msDetachStream();
// Copy the stream from the blob to the File stream
Windows.Storage.Streams.RandomAccessStream.copyAsync(input, output).then(
function () {
output.flushAsync().done(function () {
input.close();
output.close();
Windows.System.Launcher.launchFileAsync(file);
});
});
});
});
Note that CreationCollisionOption.generateUniqueName handles the file renaming automatically, so I don't need to fiddle with performance.now() as in the answer above.
Just to add that one of the things that's so difficult about UWP app development, especially in JavaScript, is how hard it is to find coherent information. It took me hours and hours to put the above together from snippets and post replies, following false paths and incomplete MS documentation.

You will want to use the PDF APIs https://github.com/Microsoft/Windows-universal-samples/tree/master/Samples/PdfDocument/js
https://github.com/Microsoft/Windows-universal-samples/blob/master/Samples/PdfDocument/js/js/scenario1-render.js
Are you simply just trying to render a PDF file?

Is it possible to retrieve text files from HTML app directory without HTTP request or <input>?

I'm working on an HTML/javascript app intended to be run locally.
When dealing with img tags, it is possible to set the src attribute to a file name with a relative path and thereby quickly and easily load an image from the app's directory. I would like to use a similar method to retrieve a text file from the app's directory.
I have used TideSDK, but it is less lightweight. And I am aware of HTTP requests, but if I remember correctly only Firefox has taken kindly to my use of this for local file access (although accessing local images with src does not appear to be an issue). I am also aware of the FileReader object; however, my interface requires that I load a file based on the file name and not based on a file-browser selection as with <input type="file">.
Is there some way of accomplishing this type of file access, or am I stuck with the methods mentioned above?

The browser will not permit you to access files like that but you can make javascript files instead of text files like this:
text1.js:
document.write('This is the text I want to show in here.'); //this is the content of the javascript file
Now call it anywhere you like:
<script type="text/javascript" src="text1.js"></script>

There are too many security issues (restrictions) within browsers making many local web-apps impossible to implement so my solution to a similar problem was to move out of browsers and into node-webkit which combines Chromium + Node.js + your scripts, into an executable with full disk I/O.
http://nwjs.io/

[edit] I'm sorry I thought you wanted to do this with TideSDK, I'll let my answer in case you want to give another try to TideSDK [/edit]
I'm not sure if it's what you're looking for but I will try to explain my case.
I've an application which allow the user to save the state of his progress. To do this, I allow him to select a folder, enter a filename and write this file. When the user open the app, he can open the saved file, and get back his progress. So I assume this enhancement is similar of what you are looking for.
In my case, I use the native File Select to allow the user to select a specific save (I'm using CoffeeScript) :
Ti.UI.currentWindow.openFileChooserDialog(_fileSelected, {
title: 'Select a file'
path: Ti.Filesystem.getDocumentsDirectory().nativePath()
multiple: false
})
(related doc http://tidesdk.multipart.net/docs/user-dev/generated/#!/api/Ti.UI.UserWindow-method-openFileChooserDialog)
When this step is done I will open the selected file :
if !filePath?
fileToLoad = Ti.Filesystem.getFile(scope.fileSelected.nativePath())
else
fileToLoad = Ti.Filesystem.getFile(filePath)
data = Ti.JSON.parse(fileToLoad.read())
(related doc http://tidesdk.multipart.net/docs/user-dev/generated/#!/api/Ti.Filesystem)
Please note that those snippets are copy/paste from my project and they will not work without the rest of my code but I think it's enough to illustrate you how I manage to open a file, and read his content.
In this case I'm using Ti.JSON.parse because there is only javascript object in these files but in your case you can just get the content. The openFileChooserDialog isn't mandatory, if you already know the file name, or if you get it from another way you can use Ti.Filesystem in your own way.