A utility class providing type-safe predicate functions for common value checks.

Installation

npm install @bisham/predicates

Usage

import { Predicates } from '@bisham/predicates';

// Type-safe checks
if (Predicates.isString(value)) {
  // TypeScript knows value is string here
  console.log(value.toUpperCase());
}

Available Methods

| Method | Signature | Description | |--------|-----------|-------------| | Type Checks | | isString | (value: unknown): value is string | Checks if value is a string | | isEmptyString | (value: unknown): value is "" | Checks if value is an empty string | | isNotEmptyString | (value: unknown): value is string | Checks if value is a non-empty string | | isNumber | (value: unknown): value is number | Checks if value is a number | | isBoolean | (value: unknown): value is boolean | Checks if value is a boolean | | isFunction | (func: unknown): func is Function | Checks if value is a function | | isObject | (value: unknown): value is Record<string, unknown> | Checks if value is an object (not null) | | isDate | (value: unknown): value is Date | Checks if value is a Date instance | | Null/Undefined Checks | | isNull | (value: unknown): value is null | Checks if value is null | | isUndefined | (value: unknown): value is undefined | Checks if value is undefined | | isEmpty | (value: unknown): value is null \| undefined | Checks if value is null or undefined | | isNotEmpty | (value: unknown): value is {} | Checks if value is neither null nor undefined | | Array Checks | | isEmptyArray | (value: unknown): value is [] | Checks if value is an empty array | | isNotEmptyArray | (value: unknown): value is Array<unknown> | Checks if value is a non-empty array | | Object Checks | | isEmptyObject | (value: unknown): value is Record<string, unknown> | Checks if value is an object with no properties | | Date Checks | | isValidDateString | (value: unknown): value is string | Checks if value is a valid date string | | Environment Checks | | isBrowser | (): boolean | Checks if current environment is a browser | | isOnline | (): boolean | Returns online status (browser) or false (Node.js) |

Examples

import { Predicates } from '@bisham/predicates';

// Type guards with TypeScript narrowing
const value: unknown = "hello";

if (Predicates.isString(value)) {
  // TypeScript knows value is string
  console.log(value.length); // ✅ Works
}

// Check for empty values
if (Predicates.isEmpty(userInput)) {
  console.log("Input is required");
}

// Check arrays
if (Predicates.isNotEmptyArray(items)) {
  // TypeScript knows items is Array<unknown>
  items.forEach(item => console.log(item));
}

// Environment checks
if (Predicates.isBrowser()) {
  console.log("Running in browser");
}

if (Predicates.isOnline()) {
  console.log("User is online");
}