@philiprehberger/type-check

Runtime type checking utilities with TypeScript type guards — typeof on steroids

Installation

npm install @philiprehberger/type-check

Usage

Basic Guards

import { isString, isNumber, isPlainObject } from '@philiprehberger/type-check';

isString('hello'); // true
isString(42);      // false

isNumber(3.14);    // true
isNumber(NaN);     // false

isPlainObject({ a: 1 }); // true
isPlainObject([]);        // false

Type Narrowing

import { isString, isNumber } from '@philiprehberger/type-check';

function format(value: unknown): string {
  if (isString(value)) {
    return value.toUpperCase(); // TypeScript knows value is string
  }
  if (isNumber(value)) {
    return value.toFixed(2); // TypeScript knows value is number
  }
  return String(value);
}

isEmpty

import { isEmpty } from '@philiprehberger/type-check';

isEmpty('');          // true
isEmpty([]);          // true
isEmpty({});          // true
isEmpty(new Map());   // true
isEmpty(null);        // true

isEmpty('hello');     // false
isEmpty([1, 2]);      // false
isEmpty({ a: 1 });   // false

API

| Function | Returns true for | | --- | --- | | isString(value) | string values | | isNumber(value) | number values (excludes NaN) | | isBoolean(value) | boolean values | | isBigInt(value) | bigint values | | isSymbol(value) | symbol values | | isFunction(value) | Functions | | isUndefined(value) | undefined | | isNull(value) | null | | isNullish(value) | null or undefined | | isPlainObject(value) | Plain objects ({}, Object.create(null)) | | isArray(value) | Arrays | | isTypedArray(value) | Typed arrays (Uint8Array, Float64Array, etc.) | | isDate(value) | Valid Date instances | | isRegExp(value) | RegExp instances | | isError(value) | Error instances (including subclasses) | | isMap(value) | Map instances | | isSet(value) | Set instances | | isPromise(value) | Promise instances or thenables with catch | | isIterable(value) | Objects with Symbol.iterator | | isAsyncIterable(value) | Objects with Symbol.asyncIterator | | isEmpty(value) | Empty strings, arrays, objects, maps, sets, or nullish |

Development

npm install
npm run build
npm test

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License

MIT