Chrome developer tools in Qlik Sense extension development (part 1)

Perhaps the most important tool for a Qlik Sense extension developer is Chrome developer tools. You can use any text editor to write your code, or even Qlik Sense dev-hub for simple extension, but you really need to use Developer Tools. Debug your code, check loading of javascript, HTML and CSS, inspect HTML structure and CSS rules – there is a lot you need to use them for. So good knowledge of them is essential.

Always run Qlik Sense in a browser

Qlik Sense Desktop is a good tool for your extension development in most scenarios. But you should never use the browser bundled with it for development. Instead use Chrome, and use http://localhost:4848/hub to access the hub. This means you will have the full developer tools available, and also that you will have an up-to-date Chrome installation.

While the browser bundled with Qlik Sense Desktop is built on the same codebase, it is not updated, but will contain an old version. It looks like the Chrome version bundled with Qlik Sense Desktop September 2019 is Chrome/47.0.2526.16 while my browser Chrome version is Chrome/78.0.3904.70, so Qlik Sense Desktop is way behind. BTW Qlik Sense Desktop also reports my Windows version as ‘Windows NT 6.1’ while Chrome proper reports the real value ‘Windows NT 10.0’.

So now that you are happily in Chrome you need to open the Developer Tools. There are different ways to do that:

• press Shift+Ctrl i (for inspect, this is the method I use)
• from Chrome menu in the top right corner, under ‘Other tools’

When doing extension development, always keep the console open. We’ll come to why later.

Disable caching

When doing extension development, you want Qlik Sense to allways load the latest version of your code. The browser normally tries to cache loaded files, and not request the file from the server again, it it already has it in memory. The first thing you should do is to disable this caching.It’s easy to do:

• open developer console
• switch to network tab
• click the ‘Disable cache’ checkbox

The disable cache checkbox only affects the browser when the developer console is open. When the developer console is not open, the browser will still cache javascript files. This is why you should always open the browser console when your are working with extension development.

Check installed extensions (and mashups)

There is a lot of information in the network tab. You can se all network requests made by the Qlik Sense client, and since the client is load in chunks there will be a lot of them. There are also requests for images, CSS stylesheets and other requests. To help you filter the requests there is a bar:

Click on XHR and you will get a list of other calls. One of them is of special interest when you are doing extension development, the one called schema (url is really /qrs/extension/schema). Click on that one, and then on ‘Preview’ and you will get a list of all extensions and mashups installed on the system, including all data in the qext file:

This is a good place to check that your extension is installed, and what version (just remember to keep the version number in the qext file up to date). It’s also a good place to start when you are troubleshooting an extension you did not write.

Debugging the extension code

The ‘Sources’ tab is what you use for debugging. If the code is minified (many extensions are) you can click the curly braches in the bottom left corner to get a somewhat more readable format.

The toolbar in the upper right corner can be used to step through your code. The stop button will make the browser pause when an error occurrs, which is very useful to find bugs. Unfortunately it does not really work in extensions. That’s because Qlik Sense catches all extension errors (and silently ignores them).

So to have the browser pause on your errors, you need to check the box ‘Pause on caught exceptions’. If you do that, the browser will pause when an exception is thrown from your code. Unfortunately it will also break on some exceptions (in libraries) that are perfectly OK, so you can’t really turn it on always. Just turn it on when you think there might be an exception thrown from your code and then trigger a repaint, for example by resizin the window.

Check files in extension

The navigator on the left side in the sources tab shows you extension files in a tree structure. But it will only show you javascript files, so CSS and HTML files are not included. If you want to see those, switch to the network tab, and filter on the extension name.

Note that the qext file is not included. That’s because the qext file is not loaded by the client, the information is instead included in the schema.

and there’s more

Of course there is more, but I couldn’t cover everything in one post. Look out for part 2, available when I find the time to write it..