Develop Reference

WebKit alternative for on Apple Watch? evaluateJavaScript()

I have a webpage and I want to interact via JavaScript with it (to get data and to perform input events) that means I want to load the webpage in background.
In iOS i could do this easily with WebKit and a webView + the evaluateJavaScript Method, but since I want to run this on Apple Watch and the fact that there isn't a WebKit framework for watchOS, I am looking for another way to do this.
Any ideas?

There is no way to run JavaScript code on watchOS at the moment. You should either port the code to Swift/Obj-C and run it natively on watchOS or you have to run the JS code in the iOS app, then send over the evaluated data to the Watch app using the WatchConnectivity framework.
Since there is no web browser on watchOS (and most likely there won't be one in the near future either), there would be no point in porting the WebKit framework to watchOS, so I suggest you find a permanent alternative for your problem.

As of watchOS 5:
Apple has ported WebKit to watchOS, which opens up a lot of possibilities. You can view web content from your watch.
Source: Apple introduces watchOS 5 | TechCrunch

Distribute Single Page Application as native desktop software

Is it possible to pack s single page application (its JavaScript files and images and all the assets) so that it can be distributed as a native
desktop application? Like having an instance of Chrome without any button that just runs your application offline.
I've used software that seems to be crafted like that, for example TweetDeck by Twitter gives me the impression of being just the web-version of TweetDeck packed in some way to run in a context that is not your standard browser.

You can use NW.js (previously Node WebKit) or Electron to do just that.

There's NW.js.
To package nodejs / html apps on the desktop.

You can do it by implementing a headless browser application.
There is an open source web browser engine here https://www.webkit.org/.
You incorporate it in a native application and parse the source files.
The webkit documentation presumably contains the specifics, have fun :)

Very much possible and all HTML5 apps are doing that, all your need is this:
https://cordova.apache.org/

Can a web application be converted to a google chrome application?

We have a very simple digital signage application that loads six web pages and rotates through them in an iframe.
We thought we would like to take this application and run in kiosk mode as a chromium app. However, simply using the HTML in the page has thrown all kinds of errors for the app. The most consistent on is the illegal use of external images, css, and fonts as well as complaints about javascript libraries, etc.
It looks as though it will be extremely painful to try to make this into a kiosk app.
Is it possible to make this type of conversion?
Does anyone have advice as to how to proceed?
Can you pull in external pages into a Chromium app?

You cannot run Javascript on a browser via local filesystem for security reasons. But what you could do is package the web app as a local app.
One option is to use Windows HTML Application (HTA)
http://en.wikipedia.org/wiki/HTML_Application
But this requires Internet Explorer to run.
Another option that sounds great is using Node Webkit. I have never done it before, but seems very powerful.
https://www.npmjs.com/package/nodewebkit
You can write a powerful Javascript app and run it locally this way.
UPDATE
Official Node Webkit website:
http://nwjs.io/

Does it make sense to use Cordova or PhoneGap for the development of a pure browser-based web application?

At first glimpse Cordova and PhoneGap exist primarily for the use to develop apps to be used on a mobile device. Well, I am not interessted in the developement of native mobile apps.
There exists a webapplication (a cms) of our own and the question is now if a mobile toolkit like Cordova or PhoneGap is able to be of any help to develop parts of our cms functionalities with it in order to be able to support more plattforms.
Does it make sense to use Cordova or PhoneGap for the developement of a pure browser-based web application?

Phonegap (or Cordova as its now called) works by wrapping your webpages in a Webview and giving you access (in JavaScript) to some of the native device functions, such as the Camera, Accelerometer, Contacts etc.
As for whether it will help you depends on if want to make use of any of the native device functions, for example if you think incorporating the Camera (current HTML support for camera is quite spotty) into your web app is of use then you probably should consider it.
Another consideration is how your users will access the applications, with Phonegap it gets packages into a native app and they can just launch it from their home-screen (or however they launch apps on their mobile device), while with a Web App it depends on the device, on iOS you can pin it to your home screen and add some meta tags to make it appear more native like (for example hide the address bar) while on Android as far as I know you can't do that.
Finally consider that with Phonegap it might be more of a pain to debug your application since your HTML/Js is wrapped in a Webview, but as far as I've seen there is no easy way to debug it there.
One other thing I seem to recall reading somewhere that on iOS Apple doesn't give your native applications' Webviews access to the same amount of memory as if it were in safari so the exact sane web application when packaged into a Phonegap application might actually be slower.
To sum up, the benefits of wrapping your application in a Phonegap wrapper are access to native device functions and how your users access your app, if those aren't important (or the cons outweigh the benefits) than it probably isn't worth your while to go that route.

Cordova/Phonegap extend javascript with functionality provided by mobile operating systems. Therefore apps developed with these frameworks must be compiled to the target platform and only embed the HTML etc. in an embedded browser. The extensions need java, objective-c etc. code to run so I don't think that you are able to benefit from this code.
You are forced to write your own mobile device compliant HTML code when using Cordova/Phonegap. There are no neat mobile device ready user interface controls provided by the framework but only access to device specific hardware or software apis like notification etc. is given.

Cordova is just the latest name of PhoneGap. I would not go for that if you just want to build a mobile website. First of all publishing such an app on several online stores (iTunes, Play) is a pain.

Writing apps for Apple platforms with Javascript

Does Apple allow iOS and Mac apps to use Javascript? Can someone give me examples of how to use it and the advantages and disadvantages?

If you're looking for a less techy solution, you could also use AppFurnace ( http://www.appfurnace.com ) to create JavaScript & HTML5 apps, packaged as native apps for iPhone and Android. We use PhoneGap (mentioned above), with an added drag-and-drop interface, enabling you to make your own apps.

You can use phonegap as a javascript, html and css wrapper in your ios app if you want to create a native app using html and javascript.

There's NimbleKit which allows you to make native apps using HTML and Javascript. Otherwise you can use a UIWebview which you can execute Javascript in. Look at the UIWebView documentation for more info.

There are tools to code your app in javascript and compile it into native code.
But if you want your app to load javascript code at runtime and run it, then see this for more details.