yummies/type-guard

Description

Runtime type guards and narrowers for primitives, DOM nodes, NaN, and common app values. Each helper is implemented once with consistent typeof / Object.prototype.toString logic so unknown from JSON, events, or third-party scripts becomes safe typed branches without ad-hoc checks scattered through the codebase.

Usage

import { typeGuard } from "yummies/type-guard";

typeGuard.isDefined()

Checks that a value is neither null nor undefined.

Examples:

isDefined(0); // true

isDefined(null); // false

typeGuard.isTruthy()

Checks whether a value is truthy (!!value).

Examples:

isTruthy(1); // true

isTruthy(0); // false

typeGuard.isFalsy()

Checks whether a value is falsy (!Boolean(value)).

Examples:

isFalsy(null); // true

isFalsy("x"); // false

typeGuard.isNull

Checks whether a value is exactly null.

Examples:

isNull(null); // true

isNull(undefined); // false

typeGuard.isUndefined

Checks whether a value is exactly undefined.

Examples:

isUndefined(undefined); // true

isUndefined('value'); // false

typeGuard.isObject

Checks whether a value is a plain object.

Examples:

isObject({ id: 1 }); // true

isObject([]); // false

typeGuard.isArray

Checks whether a value is an array.

Examples:

isArray([1, 2, 3]); // true

isArray({ length: 1 }); // false

typeGuard.isString

Checks whether a value is a string object or primitive string.

Examples:

isString('hello'); // true

isString(123); // false

typeGuard.isNumber

Checks whether a value is a finite number.

Unlike isNaN and isInfinite, this guard only matches regular numeric values.

Examples:

isNumber(123); // true

isNumber(Number.NaN); // false

typeGuard.isBoolean

Checks whether a value is a boolean.

Examples:

isBoolean(true); // true

isBoolean('true'); // false

typeGuard.isFunction

Checks whether a value is a synchronous or asynchronous function.

Examples:

isFunction(() => {}); // true

isFunction(async () => {}); // true

typeGuard.isRegExp

Checks whether a value is a regular expression.

Examples:

isRegExp(/foo/); // true

isRegExp('foo'); // false

typeGuard.isElement

Checks whether a value looks like a DOM element or document node.

Examples:

isElement(document.body); // true

isElement({ nodeType: 3 }); // false

typeGuard.isNaN

Checks whether a value is NaN.

Examples:

isNaN(Number.NaN); // true

isNaN(5); // false

typeGuard.isInfinite

Checks whether a value is positive or negative infinity.

Examples:

isInfinite(Infinity); // true

isInfinite(10); // false

typeGuard.isSymbol

Checks whether a value is a symbol.

Examples:

isSymbol(Symbol('id')); // true

isSymbol('id'); // false