@zokugun/is-it-type

Why @zokugun/is-it-type?

• Zero dependencies.
• Predictable naming across primitives, boxed types, iterables, errors, promises, and constructors.
• First-class TypeScript support: every helper is a ready-to-use predicate.
• typeOf/isType go beyond native typeof, normalizing async vs. sync functions, arrays vs. records, Node.js errors, and more.

Getting Started

With node previously installed:

npm install @zokugun/is-it-type

Import only the predicates you need (tree-shaking friendly) and use them as runtime guards:

import { isNonEmptyArray, isString } from '@zokugun/is-it-type';

function normalizeTags(input: unknown): string[] {
    if(!isNonEmptyArray(input)) {
        return [];
    }

    return input.filter(isString);
}

Usage Examples

Narrowing unknown data

import { isRecord, isBooleanLike, isNonNull, toBoolean } from '@zokugun/is-it-type';

function readFeatureFlag(payload: unknown): boolean {
    if(isRecord(payload) && isBooleanLike(payload.enabled)) {
        return toBoolean(payload.enabled);
    }

    return false;
}

Classifying values with typeOf and isType

import {typeOf, isType} from '@zokugun/is-it-type';

const kind = typeOf(value);

switch(kind) {
    case 'array':
        // Guaranteed array here
        break;
    case 'async-function':
        await value();
        break;
    default:
        // Handle primitives, records, promises, etc.
}

if(isType(value, 'date')) {
    console.log('Timestamp:', value.getTime());
}

typeOf returns normalized descriptors beyond the native typeof, including: array, record, date, error, node-error, promise, regexp, async-function, sync-function, constructor, and generator, plus the standard primitives (undefined, null, boolean, number, bigint, string, symbol). Combine it with isType for expressive guards without duplicating comparison logic.

Quick Reference

| Predicate | What it checks | | ------------------------- | --------------------------------------------------------------------------------------------------- | | isActualFunction | Raw typeof value === 'function' check (constructors/classes pass). | | isActualObject | Non-null values whose typeof is 'object' (arrays included). | | isArray | Array.isArray plus an optional per-element predicate. | | isAsyncGenerator | Functions whose constructor name is AsyncGeneratorFunction. | | isAsyncIterable | Objects implementing Symbol.asyncIterator. | | isAsyncFunction | Functions whose constructor name is AsyncFunction. | | isBigInt | Primitive bigint values. | | isBigIntLike | Primitive bigint or boxed BigInt objects. | | isBlankString | Strings that become empty after trim(). | | isBoolean | Primitive booleans. | | isBooleanLike | Primitive booleans or boxed Boolean objects. | | isBoxedBigInt | Boxed BigInt objects. | | isBoxedBoolean | Boxed Boolean objects. | | isBoxedNumber | Boxed Number objects. | | isBoxedPrimitive | Boxed BigInt, Boolean, Number, or String objects. | | isBoxedString | Boxed String objects. | | isConstructor | Functions whose prototype indicates they should be called with new. | | isDate | instanceof Date. | | isEmptyArray | Arrays whose length is 0. | | isEmptyRecord | Plain objects with no own enumerable keys. | | isEmptyString | Strings of length 0. | | isError | instanceof Error. | | isFinite | Number-like inputs that are neither NaN nor ±Infinity. | | isFunction | Callables that are not constructors/classes. | | isGenerator | Functions whose constructor name is GeneratorFunction or AsyncGeneratorFunction. | | isInteger | Values where Number.isInteger(value) succeeds. | | isIntegerGreaterOrEqual | Integers greater than or equal to the provided threshold. | | isIntegerGreaterThan | Integers strictly greater than the provided threshold. | | isIntegerLessOrEqual | Integers less than or equal to the provided threshold. | | isIntegerLessThan | Integers strictly less than the provided threshold. | | isNaN | Number-like inputs whose numeric value is NaN. | | isIterable | Objects implementing Symbol.iterator or Symbol.asyncIterator. | | isNegativeInteger | Integers strictly below zero. | | isNegativeIntegerOrZero | Integers that are zero or below. | | isNodeError | Objects matching NodeJS.ErrnoException shape (they expose code). | | isNonBlankString | Strings containing non-whitespace characters. | | isNonEmptyArray | Arrays with at least one element. | | isNonEmptyRecord | Plain objects that own at least one key. | | isNonEmptyString | Strings whose length is greater than 0. | | isNonNull | Values that are not strictly null. | | isNonNullable | Values excluding both null and undefined. | | isNonUndefined | Values that are not undefined. | | isNull | Strict null checks. | | isNullable | Values that are either null or undefined. | | isNumber | Primitive numbers (including NaN/Infinity). | | isNumberLike | Number or bigint primitives plus boxed Number/BigInt objects. | | isObject | Non-null objects that are not arrays. | | isObjectLike | Non-null objects or functions. | | isPositiveInteger | Integers strictly above zero. | | isPositiveIntegerOrZero | Integers that are zero or above. | | isPrimitive | String, number, boolean, or bigint primitives. | | isPromiseLike | Objects exposing a callable then method. | | isPromise | Objects whose constructor is Promise. | | isRecord | Plain objects (default Object constructor, not arrays/arguments). | | isRegExp | instanceof RegExp. | | isString | Primitive strings. | | isStringLike | Primitive strings or boxed String objects. | | isSyncGenerator | Functions whose constructor name is GeneratorFunction. | | isSyncIterable | Objects implementing Symbol.iterator. | | isSymbol | Primitive symbols. | | isSyncFunction | Functions that are neither constructors, async, nor generator functions. | | isType | Wrapper that compares typeOf(value) to a TypesLiteral. | | isUndefined | Strict undefined checks. | | typeOf | Normalized typeof replacement (array, record, async-function, constructor, etc.). | | toBigInt | Returns the primitive bigint value from either a primitive or BigInt wrapper. | | toBoolean | Returns the primitive boolean value from either a primitive or Boolean wrapper. | | toNumber | Returns the primitive number value from either a primitive or Number wrapper. | | toPrimitive | Unboxes any boxed primitive (Boolean, Number, String, BigInt) to its primitive counterpart. | | toString | Returns the primitive string value from either a primitive or String wrapper. |

Need a normalized descriptor instead of a boolean? Reach for typeOf helper function and the Types/TypesLiteral TypeScript helpers.

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License

Copyright © 2025-present Baptiste Augrain

Licensed under the MIT license.