We Keep Coding

Blocking websites on a web app using javascript

I'm currently developing a web app that allows users to add a list of websites that they want to block i.e. preventing them from accessing the website from their browser.
Ideally I want to be able to block websites on every browser but this is difficult, so I narrowed my research to just Chrome for now. I came across the chrome.webRequest api which seems promising but it specifically says its for chrome extensions and am unsure if it would work for my web app.
Can anyone point me in the right direction for blocking websites on a web app, ideally using javascript. Any help is much appreciated!!
EDIT:
1) I forgot to mention that I'm using firebase for my backend.
2) People have been saying that I can't block websites outside the web apps scope, if I instead used electron to make the web app a desktop application would it then be possible?

Firstly you have a database containing URL of blocked websites. URLs are modified using your web app. That's one part. Now your problem is how to make the browser work with your database.
The only possible way for you to share blocked URLs with the browser is via API. You must have API that can communicate outside your web app.
Now browsers such as chrome/firefox give users the power to make changes inside and outside the dom. For chrome, you have chrome extension where Google provides API so the users can manipulate actions outsides regular actions such as manipulating dom. An example I can give that is closely related to your subject matter, which is an action activated before/after a user enters URL on the search box and for that, we use the following API from https://developer.chrome.com/extensions/webRequest
And it's same for Firefox.

Capture web page data using native language code

I'm looking for leads on how to capture web page metadata from the current browser page. I want to create a feature in my application that will allow the user to press a hot key and record meta data from the web page currently open in the user's browser. My application will be running minimized, this feature is to be activated by a global hot key.
I'm using nw.js (formerly Node-Webkit) to create this application, so ideally, the solution would be javascript running in a desktop installation of Node.js. If this is not practical, I understand that I can call platform specific code from nw.js, so solutions developed in any desktop os language would be of interest.
My application targets OS X and Windows.
I'm hoping to capture metadata from all major modern browsers (Chrome, Firefox, Safari and IE 10+).
At a minimum I need to capture the page url, but I also want to capture Keywords, Description and highlighted text for the source web page.
I need to implement this function without modifying the source webpage in any way, and I prefer to avoid the need for browser extensions, bookmarklets or plugins.
If a solution exists using a remote controlled browser extension (no user interaction) that would be of interest, but ideally I want to avoid requiring the end user to install or interact with anything but my application.
My search to date has located no information on reading web page information from applications outside the browser.
Any thoughts or leads are much appreciated.

Strange website redirect issue on mobile browser that's influenced by cache

I'm at a loss here.
I have a new Wordpress site at synergration.com.
If you access it on a mobile device (phone, not tablet) it will generally load fine the first time. Once you click on to another page and/or reload the home page it jumps into a redirect loop indefinitely attempting to reload the same page over and over and over...
I've weeded through the code and have been unable to find any JS redirects. I've also contacted the theme developer and they've been unable to help.
This only became an issue when I started hosting on WP Engine. They use some advanced caching that seems to be the culprit here as when I test the mobile site on their staging server (where no cacheing exists) it loads fine.
I contacted WPEngine about it and this was their reply:
This is being caused by our caching systems that run on our platform.
It looks like the theme is handling an internal redirect that detects
the user agent (desktop or mobile) and redirects the visitor to the
appropriate site based on that information. However, the redirect is
getting stuck in cache, causing the mobile version to load in an
infinite loop. Unfortunately, we don’t have an easy solution for this.
If this were only one part of the site, we could just exempt that part
of the site from caching, but because it covers the whole site,
exempting from caching isn’t an option. Our staging area is exempt
from all caching, which is why it’s working normally there. (The old
host was most-likely using a non-cached environment, which is why you
didn’t see this issue there). I would contact the theme developer and
ask them if they’ve ever come across this issue before. There’s a good
chance they have, and they might have a clever solution as a
work-around. You might have the option of disabling the mobile
routing, which would solve the redirect issue, though mobile devices
would load the full version of the site rather than the slimmed-down
mobile version.
As noted above, the theme developer didn't have any solution and I'm back at square one so I figured I'd reach out to stack to see if ya'll had any ideas.

I have two sites on WP Engine with redirect. They are identical gensis child themes and redirect plugins. I have one setup with a DNS redirect to a cname record for a "M.sitename.com" URL and the other redirecting to the mobile site that is having the same issue you noted above. I haven't had an issue with the site that points to the cname record. I am about the change the other site to the cname configuration to see if it makes a difference. I have no ideal why this works, but thought you might find this of value.

It works absolutely fine in my mobile's Opera Mini browser. To answer your question, an alternative way is to just create a mobile subdomain, like m.yourdomain.com. Make this decision public and let mobile users know in advance that that is the site for mobile users. A specific mobile site is loads better than visiting the page and then being redirected. It also saves time.
While developing the mobile site, keep in mind, to use minimal JavaScript. The reason being, that older mobile versions may not support JavaScript and if JavaScript is essential then it becomes a big problem.
Speaking about the theme, if it is getting stuck and developer has no idea, so the best option, FOR NOW, is change the template. Let the developer inspect on his very code. You can by that time use another template, that'll keep the site up running well whether it is on Mobile or anything. Because, small errors can divert lot of traffic from your site. I, to be frank, have no idea about what caching problems WP is having, and I don't expect anyone here to be knowing that, so it really depends on time. Till then, as I said, do try to use some other template for the time-being.
All the best.

I faced similar issue recently. It took good amount of time but I finally figured it out.
To prevent redirect from caching, you have to use 302 redirect. Moreover, you have initialize this redirect in "template_redirect" action of wordpress. If you do it in like "init", it'll be cache too.

Launch mobile Safari from UIWebView *without* modifying app source?

I'm developing a small site that will only be viewed in-app inside a UIWebView, and one page has several links to an external website. I'd like these to open in mobile Safari, but all links inside the app load within the webview. Modifying the source of the app isn't an option since the site needs to be live before any changes could be submitted.
Is there a way to force a link inside a UIWebView to launch mobile Safari using HTML/5 or Javascript? Mimic shouldStartLoadWithRequest? Sneaky, hacky workarounds or brilliant alternate solutions?
(And, out of sheer curiosity... why not?)

It would be bad design to let sites access the frameworks on the iPhone via simple HTML. This would open up all sorts of security holes. Its not web behavior you want to alter, so I think you may need to change the app source. I still don't understand why that isn't an option. Could you go into more depth?

One option would be to add a custom URL handler. Your website could then determine if the "broswer" is the app and serve custom URLs for those links you'd like to maintain (aka open) in your app. Then, any standard HTTP/s URLs would open in Mobile Safari.
In other words, have your web server provide urls like myappurl:// for the links you'd like your app to handle, and http:// which would open Mobile Safari.

What is the best way for a website to check if a user has installed a client app?

Let's say I've got a website that works better if a client has installed and logged into a desktop application. I'd like to be able to do 2 things:
Alter the website if they haven't installed the app (to make it easy for them to find a link to the installer)
If they've installed the app on a couple of machines, determine which machine they are browsing from
I'd like something that works on Windows and OSX, on any of the major browsers. Linux is a bonus.
A few thoughts:
Websites can detect if you've got Flash installed. How does that work and could it be used for both of my goals?
Could I just let the client serve HTTP on localhost and do some javascript requests to fetch a local ID? I know google desktop search did something like this at one point. Is this a standard practice?
Thanks!

You can register a protocol from your desktop application (see this). This can be used, for example, to open your desktop application with arbitrary data from the website. You could then have your desktop app send a HTTP request to your webserver, telling it what machine you are on.

You can have a browser plugin (activex for IE or Netscape plugin for the rest of the browsers) that can communicate with the application. When the webpage is loaded, it can try to instantiate the plugin and if it succeeded, it can use it as a proxy to the application. If it fails, then either the app is not installed or the plugin was explictly disabled by the user. Either way, your website should degrade its functionality accordingly.
Update: Forgot to answer your questions:
Flash does it exactly this way. Flash is a browser plugin that is created by the web pages.
You can have a machine ID generated at the application/plugin install time and your plugin can pass that machine ID to the webpage when it is created.
On the topic of using local webserver:
I would stay away from having a local webserver, mainly because of security considerations. It takes quite a lot of work to make sure your local webserver is locked down sufficiently and there are no XSS vulnerabilities that other malicious websites can exploit to make it do stuff on their behalf.
Plus, having a webserver means that either it has to run as a system-wide process, or if it runs as the user, you can have the website interact with only one user's instance of the application, even though multiple users can be logged on and running it at the same time.
Google Desktop Search suffered from both the XSS security vulnerability (though they fixed it) and the limitation of only one user being able to use it on a machine (I don't know if they fixed this one yet, though chances are they did).

Websites can detect if you've got Flash installed.
Actually, I believe a browser can detect if you have the Flash plugin for the browser installed, and webpages can offer "installed" and "uninstalled" option that the browser can choose.
Otherwise, you are asking for a means, by putting some code in a webpage, of being able to analyze a user's home computer, and report what it learned to you website.
Can you say Major Security Hole?

If you can pick a development environment for the desktop app, then check out AIR from Adobe. It lets you develop desktop applications using either html/javascript, Flash, or Flex.
It has API calls you can use from a browser based flash app to see if the desktop based AIR app is installed, what version, etc. You can even launch it and pass parameters from the web app to the desktop app.
http://www.rogue-development.com/blog2/2008/03/interacting-with-an-air-app-from-a-browser-based-app/

Websites can detect if you've got Flash installed. How does that work and could it be used for both of my goals?
it's quite a bit simple, your browser tries to render some additional files, with some specific formats such as flash .swf and I the browser doesn't find installation, then will be start downloading, or you will get the option to download that program.
Flash also uses AC_RunActiveContent.js please take a look at this js, people usually put this on their webpages
if (AC_FL_RunContent == 0) {
alert("This page requires AC_RunActiveContent.js.");
} else {
AC_FL_RunContent( 'codebase','http://download.macromedia.com/pub/shockwave cabs/flash swflash.cab#version=8,0,0,0','width','981','height','635','id','build5','align','middle','src','build5','quality','high','bgcolor','#ffffff','name','build5','allowscriptaccess','sameDomain','allowfullscreen','false','pluginspage','http://www.macromedia.com/go/getflashplayer','movie','build5' ); //end AC code
}