The call `arr[2]()` is syntactically the good old `obj[method]()`, in the role of `obj` we have `arr`, and in the role of `method` we have `2`.

So we have a call of the function `arr[2]` as an object method. Naturally, it receives `this` referencing the object `arr` and outputs the array:

```js run
let arr = ["a", "b"];

arr.push(function() {
  alert( this );
})

arr[2](); // "a","b",function
```

The array has 3 values: initially it had two, plus the function.