Using non-null assertions cancels out the benefits of strict null-checking, and introduces the possibility of runtime errors. Avoid non-null assertions unless absolutely necessary. If you still need to use one, write a skipcq comment to explain why it is safe.

Ideally, you want to have a validation function that confirms a value isn't null, with a return type like this:

type AccentedColor = `${Color}-${Accent}`
function isColorValid(name: string): name is AccentedColor {
  // ...
}

Bad Practice

// a user named "injuly" may not exist in the DB
const injuly: User | null = db.getUserByName("injuly");

// Using the non-null assertion operator will bypass null-checking
const pfp = injuly!.profilePicture;

Recommended

const injuly: User | null = db.getUserByName("injuly");
const pfp = injuly?.profilePicture; // pfp: Image | undefined

// OR:

const pfp_ = injuly ? injuly.pfp : defaultPfp; // pfp: Image

Alternatively:

function isUserValid(userObj: User | null | undefined ): userObj is User {
  return Boolean(userObj) && validate(userObj);
}

const injuly = db.getUserByName("injuly")
if (isUserValid(injuly)) {
  const pfp = injuly.profilePicture;
  // ...
}

Moltivie / the-t3-stack

No ignore rules found