Improve code

[a2br]

Simplified and removed useless code.

• Made use of single-line if,
• forEach when for is useless,
• corrected some errors,
• simplified functions (unnecessary return => arrow functions),
• and used nullish operator ??= to avoid redundant if/else statements.

[a2br]

Oops, what a mess! I thought I could simply comment on my changes in the 'Files changed' section, but it appears it posts my comments here. Sorry, I'm not very familiar with this part of GitHub.

[mahowa]

If you could fix that one issue i will merge