(JavaScript) What structure is that?

I need to make a Fibonacci sequence and I found this code below here. When I try to understand all code, I saw "(i <= 1) ? i : arr[i-2] + arr[i-1]" I thought that was an simple if else shortcut condition, and I try to replace by the extended way just to be sure (see the last code). But now the code didn't work...

//Stackoverflow code:
function fib(n){
  return new Array(n).fill(1).reduce((arr, _ ,i) => {
      arr.push((i <= 1) ? i : arr[i-2] + arr[i-1])
      return arr
  },[]) ;
}
console.log(fib(10))

//My code with (extended if else):
function fib(n){
    return new Array(n).fill(1).reduce((arr, _ ,i) => {
        arr.push(if (i <= 1) {
            i
        } else {
            arr[i-2] + arr[i-1]            
        })
        return arr
    },[]) ;
  }
  console.log(fib(10))

Why my code do not work? Is "(i <= 1) ? i : arr[i-2] + arr[i-1]" a kind of if/else statement?