Impossible to open an external link on ios and not be stuck in a browser?

If I add a link in my ionic app like

<a href="#" onclick="'', '_system', 'location=yes');return false;"> link</a>

the web page opens and there is a button which I can click to go back to the app, however I need to load the url from a json file, event.url

the code below opens the url but leaves me stuck in the browser…
<a href="{{event.url}}" > link</a>

this code doesn’t work either
<a href="#" onclick="{{event.url}}, '_system', 'location=yes');return false;"> link</a>

I’ve also tried various solutions on the forum but nothing works!
surely this should be simple, how can I do it?