for-sample.js

function isItDone(a) {
 console.log("fn called!")
 return a < 10
}

for(let a = 0; isItDone(a); a++) {
 console.log(a)
}
/*
fn called!
0
fn called!
1
fn called!
2
fn called!
3
fn called!
4
fn called!
5
fn called!
6
fn called!
7
fn called!
8
fn called!
9
fn called!
*/