tiny-types/src/predicates/hasLengthOf.ts

A tiny library that brings Tiny Types to JavaScript and TypeScript

import { isDefined } from './isDefined';
import { isEqualTo } from './isEqualTo';
import { Predicate } from './Predicate';
import { property } from './property';

export interface HasLength { length: number; }

/**
 * @desc Ensures that the `value` is of `expectedLength`.
 * Applies to {@link String}s, {@link Array}s and anything that has a `.length` property.
 *
 * This function is an alias for to `property('length', isDefined(), isEqualTo(expectedLength))`
 *
 * @example <caption>Array</caption>
 * import { ensure, hasLengthOf, TinyType } from 'tiny-types';
 *
 * class Tuple extends TinyType {
 *   constructor(public readonly values: any[]) {
 *      super();
 *      ensure('Tuple', values, hasLengthOf(2));
 *   }
 * }
 *
 * @example <caption>String</caption>
 * import { ensure, hasLengthOf, TinyType } from 'tiny-types';
 *
 * class Username extends TinyType {
 *   constructor(public readonly value: string) {
 *      super();
 *      ensure('Username', value, hasLengthOf(8));
 *   }
 * }
 *
 * @param {number} expectedLength
 * @returns {Predicate}
 */
export function hasLengthOf(expectedLength: number): Predicate<HasLength> {
    return property('length', isDefined(), isEqualTo(expectedLength));
}