TypeScript Basics: Operators

• Operators like + and * can only be used on types that make sense. For example, we can add numbers with + and multiply with *. We can also use + to concatenate strings. However, we can't use * on strings. That's a type error.

• (Some examples in this lesson will cause a type error. For those, you should answer with type error.)

• >

  1 + 1;

  Result:

  2

• >

  2 * 2;

  Result:

  4

• >

  '1' + '1';

  Result:

  '11'

• >

  '2' * '2';

  Result:

  type error: The left-hand side of an arithmetic operation must be of type 'any', 'number', 'bigint' or an enum type.

• >

  '4' / '2';

  Result:

  type error: The left-hand side of an arithmetic operation must be of type 'any', 'number', 'bigint' or an enum type.

• In JavaScript, 'a' * 'b' is NaN. If that happens in a real system, it's almost certainly a bug. TypeScript makes this type of bug nearly impossible!

• We also can't pass mixed types to operators if they don't make sense.

• >

  1 / '1';

  Result:

  type error: The right-hand side of an arithmetic operation must be of type 'any', 'number', 'bigint' or an enum type.

• However, TypeScript will still allow some questionable combinations. For example, 1 + '1' gives '11', as in JavaScript.

• >

  1 + '1';

  Result:

  '11'

• >

  '1' + 1;

  Result:

  '11'