type numeric

@nick/is/type/numeric

IsNumeric

Signature

export type IsNumeric<T, True = true, False = false> = T extends number | bigint
  ? True
  : T extends `${number}` | `${bigint}` ? True
  : T extends `${number}${string}` ? True
  : False;

If the given string T is numeric (meaning a literal number like 0, a literal bigint like 0n, the generic types number or bigint, or generic numeric string like ${number} or ${bigint}), this type resolves to the True type parameter (defaults: true). Everything else will resolve to the False parameter (default: false).

Similar to the other utility types in this module, the parameterization of this type's conditional true and false branches allows for both simple inline conditional type checks as well as more complex nested conditionals, without the need for any x extends y ? a : b ternaries.

Type Parameters

• T
• True (default: true)
• False (default: false)

---

Category

Types

Examples

// simplified tuple traversal
declare function map<const A extends readonly unknown[], const B>(
  array: [...A],
  fn: (input: A[number], index: number) => B,
): [...{ [K in keyof A]: IsNumeric<K, B, A[K]> }];

const result = map([1, 2, 3], (x) => x * 2);
//     ^? const result: [number, number, number]