guardz/dist/typeguards/isType.d.ts

A simple and lightweight TypeScript type guard library for runtime type validation.

export interface TypeGuardFnConfig {
    readonly callbackOnError: (errorMessage: string) => void;
    readonly identifier: string;
    readonly errorMode?: 'single' | 'multi' | 'json';
}
export type TypeGuardFn<T> = (value: unknown, config?: TypeGuardFnConfig | null) => value is T;
/**
 * Creates a type guard function for validating objects against a schema.
 *
 * The data type that comes from different sources (like from server side, library, url params) is not always reliable.
 * Therefore, we need to use this function to ensure the data type is correct.
 *
 * @template T - The type to validate
 * @param propsTypesToCheck - Object mapping property keys to their type guard functions
 * @returns A type guard function that validates the object structure
 *
 * @example
 * ```typescript
 * import { isType, isString, isNumber } from 'guardz';
 *
 * interface User {
 *   name: string;
 *   age: number;
 * }
 *
 * const isUser = isType<User>({
 *   name: isString,
 *   age: isNumber,
 * });
 *
 * const data: unknown = { name: 'John', age: 30 };
 * if (isUser(data)) {
 *   // TypeScript now knows data is User
 *   console.log(data.name); // Safe to access
 * }
 * ```
 *
 * @example
 * ```typescript
 * // Nested object validation
 * interface Address {
 *   street: string;
 *   city: string;
 * }
 *
 * interface User {
 *   name: string;
 *   address: Address;
 * }
 *
 * const isAddress = isType<Address>({
 *   street: isString,
 *   city: isString,
 * });
 *
 * const isUser = isType<User>({
 *   name: isString,
 *   address: isAddress,
 * });
 * ```
 */
export declare function isType<T>(propsTypesToCheck: {
    [P in keyof T]: TypeGuardFn<T[P]>;
}): TypeGuardFn<T>;