jsschools

Literal type

A type whose only value is a specific string, number, or boolean.

Since TS 2.0 Spec ↗

Syntax

'value' | 42 | true

Examples

let dir: 'left' | 'right';
dir = 'left';
// dir = 'up'; // Error

function roll(): 1 | 2 | 3 | 4 | 5 | 6 {
  return 4;
}

const ok = true as const; // type: true

Notes

Literal types restrict a value to exact constants and are the foundation of string-union enums and discriminated unions. `const` declarations infer literal types automatically; `let` widens to the base primitive unless `as const` is used.

See also