How can I do sth before tabs change?
I think the question shouldn’t be how you do stuff before a tab changes, but how you do stuff before loading a page in a tab. A tab change always triggers a ionViewWillLoad on the page that’s at the top of the stack from the tab you’re changing to, so just use that event to do stuff when you change tabs.
If you need some more fine grained control over the tabs, you could do stuff from within your tabs.ts. Use (ionSelect) on a specific tab and do some stuff within the function in your tabs.ts. I think those two combined practically cover every use case you wan’t to handle when switching tabs. What exactly do you need to do on tabs change?