Why we write this keyword with all variable in ionic 2

Normally in android i don’t write this keyword with all but in ionic 2 i write this keyword with all variables .

why it need?

Instead of me trying to blabber on about it, here’s the docs.

thanx…mhartington
I know the use of this keyword but i want to know why need to write.
let’s take example for understand my question…basically i am android developer so in android we do not need write in all places this keyword. why in ionic we write this keyword in all places.

Because JavaScript is brain-dead.