Call an Service function ngOnInit (How to do that?) Possible?

Ionic Framework ionic-v3
1

I have a function that i want to load sometimes oninit and sometime when i click on a button.

I dont want to make the function over and over again. only one that i can chnage in.

As far i know i have made an service function that is always there.

But how do i put it on my ngOnInit??

2

What do you mean by “load” and “put it on” when referring to functions? Generally people define functions somewhere, and call them elsewhere.