It will be much easier if you will add PR description for reviewing the changes done by you .

As much I know both of the provided approaches have the same time and space complexity, as they follow the same algorithm for generating and printing Fibonacci numbers.
Can you describe properly in what aspect you want to update it

Well just because it is Javascript, May be it will not throw an error, But it can throw error in production. For example , in the place of fi=null, if we take fi=undefined, the code will also run. But, adding a primitive datatypes "fi" will make the code readable. If you think that you don't want update it its ok.