Nullish Values

null

null means there is a value, and that value is nothing.

The value is intended to be nothing...meaning it was set to nothing with intention.

const userInfo = {
  name: 'Nate',
  email: 'nate@example.com',
  secondaryEmail: null, // user has no secondary email
};

undefined

undefined means the value isn't available (yet?).

It is an unambiguous indication that there may be something different there in the future.

const formInProgress = {
  createdAt: new Date(),
  data: new FormData(),
  completedAt: undefined,
};
function submitForm() {
  formInProgress.completedAt = new Date();
}

void

void should be used exclusively to describe that a function's return value should be ignored.

console.log(`console.log returns nothing.`);
// (method) Console.log(...data: any[]): void

! - Non-null assertion operator

The non-null assertion operator (!) is used to cast away the possibility that a value might be null or undefined.

Overall recommended to NOT use this.

From the TypeScript Fundamentals, v3↗ course on FEM↗ taught by Mike North↗.