ts-is-present/lib/index.d.ts

A library to have a generic typescript definition for object presence.

export declare function isPresent<T>(t: T | undefined | null | void): t is T;
export declare function isDefined<T>(t: T | undefined): t is T;
export declare function isFilled<T>(t: T | null): t is T;
/**
 * Returns a function that can be used to filter down objects
 * to the ones that have a defined non-null value under the key `k`.
 *
 * @example
 * ```ts
 * const filesWithUrl = files.filter(file => file.url);
 * files[0].url // In this case, TS might still treat this as undefined/null
 *
 * const filesWithUrl = files.filter(hasPresentKey("url"));
 * files[0].url // TS will know that this is present
 * ```
 *
 * See https://github.com/microsoft/TypeScript/issues/16069
 * why is that useful.
 */
export declare function hasPresentKey<K extends string | number | symbol>(k: K): <T, V>(a: T & { [k in K]?: V | null | undefined; }) => a is T & { [k_1 in K]: V; };
/**
 * Returns a function that can be used to filter down objects
 * to the ones that have a specific value V under a key `k`.
 *
 * @example
 * ```ts
 * type File = { type: "image", imageUrl: string } | { type: "pdf", pdfUrl: string };
 * const files: File[] = [];
 *
 * const imageFiles = files.filter(file => file.type === "image");
 * files[0].type // In this case, TS will still treat it  as `"image" | "pdf"`
 *
 * const filesWithUrl = files.filter(hasValueKey("type", "image" as const));
 * files[0].type // TS will now know that this is "image"
 * files[0].imageUrl // TS will know this is present, because already it excluded the other union members.
 *
 * Note: the cast `as const` is necessary, otherwise TS will only know that type is a string.
 * ```
 *
 * See https://github.com/microsoft/TypeScript/issues/16069
 * why is that useful.
 */
export declare function hasValueAtKey<K extends string | number | symbol, V>(k: K, v: V): <T>(a: T & { [k in K]: any; }) => a is T & { [k_1 in K]: V; };