@typedly/array/lib/append-if-exists.type.d.ts

A TypeScript type definitions package to handle array-related operations.

/**
 * @description Appends the `Element` type to the generic type variable `Array` if `Element` already exists in the array.
 * @export
 * @template {readonly Type[]} Array
 * @template {Type} Element
 * @template [Type=any]
 * @example
 * import { AppendIfExists } from '@typedly/array';
 *
 * // Element exists in the array, so it's appended
 * type Example1 = AppendIfExists<[1, 2, 3], 2>;  // [1, 2, 3, 2]
 * const example1: Example1 = [1, 2, 3, 2];
 *
 * // Element does not exist, so the array remains unchanged
 * type Example2 = AppendIfExists<[1, 2, 3], 4>;  // [1, 2, 3]
 * const example2: Example2 = [1, 2, 3];
 *
 * // Strings work too! "b" exists, so it's appended
 * type Example3 = AppendIfExists<["a", "b", "c"], "b">;  // ["a", "b", "c", "b"]
 * const example3: Example3 = ["a", "b", "c", "b"];
 */
export type AppendIfExists<Array extends readonly Type[], Element extends Type, Type = any> = Element extends Array[number] ? [...Array, Element] : Array;