Arrow function in javascript output? [closed]

Here is the function re-written to show what is happening.

1. main takes x = 1
2. defaultFunction returns the original x = 1
3. resultFn is a function that gets called inside of main that takes x
4. y is assigned the x that was passed all the way down (local -scope) 1
5. x is reassigned to 2
6. The result is 2, 1, 1

This is an exercise on variable/parameter scope.

const main = (x) => {                      // x = 1
  const defaultFn = () => x;               // x = 1
  const resultFn = (x, f = defaultFn) => { // x = 1
    var x;                                 // x is still 1
    var y = x;                             // y = 1
    x = 2;                                 // x = 2
    return [x, y, f()];                    // x = 2, y = 1, f() -> 1
  };
  return resultFn(x);                      // 2, 1, 1
};

console.log(main(1));

You set x to 2 thus it got returned as 2. Change x to 1. Fixed Code:

console.log((function(x, f = () => x) {
  var x;
  var y = x;
  x = 2;
  return [x, y, f()];
})(1));