TypeScript Basics: Tuples

• TypeScript supports tuples, which are arrays of fixed length. For example, [number, number] is a tuple of two numbers. It must be exactly two numbers; not one and not three. If the length doesn't match, it's a type error.

• >

  let numbers: [number, number] = [1, 2];
  numbers[0];

  Result:

  1

• >

  let numbers: [number, number] = [1];

  Result:

  type error: Type '[number]' is not assignable to type '[number, number]'.
    Source has 1 element(s) but target requires 2.

• In the above error, the compiler is telling us that our tuple had only one element, at index 0. Index 1 was missing.

• Tuples can have different types in each index. This is different from arrays, where every element must have the same type.

• >

  let numberAndString: [number, string] = [1, 'a'];
  numberAndString[1];

  Result:

  'a'

• >

  let numberAndString: [number, string] = [1, 2];
  numberAndString[1];

  Result:

  type error: Type 'number' is not assignable to type 'string'.