> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/nodejs/userland-migrations/llms.txt
> Use this file to discover all available pages before exploring further.

# util.is*() Type Checks

> Migrate deprecated util.is*() methods to modern JavaScript type checking equivalents

This codemod replaces the following deprecated `util.is*()` methods with their modern equivalents.

## What It Does

This codemod handles 15 deprecated type-checking methods:

* `util.isArray()` → `Array.isArray()`
* `util.isBoolean()` → `typeof value === 'boolean'`
* `util.isBuffer()` → `Buffer.isBuffer()`
* `util.isDate()` → `value instanceof Date`
* `util.isError()` → `Error.isError()`
* `util.isFunction()` → `typeof value === 'function'`
* `util.isNull()` → `value === null`
* `util.isNullOrUndefined()` → `value === null || value === undefined`
* `util.isNumber()` → `typeof value === 'number'`
* `util.isObject()` → `value && typeof value === 'object'`
* `util.isPrimitive()` → `Object(value) !== value`
* `util.isRegExp()` → `value instanceof RegExp`
* `util.isString()` → `typeof value === 'string'`
* `util.isSymbol()` → `typeof value === 'symbol'`
* `util.isUndefined()` → `typeof value === 'undefined'`

## Before/After Examples

### Type Checks

**Before:**

```javascript theme={null}
const util = require('node:util');

if (util.isArray(value)) { }
if (util.isString(value)) { }
if (util.isNumber(value)) { }
```

**After:**

```javascript theme={null}
if (Array.isArray(value)) { }
if (typeof value === 'string') { }
if (typeof value === 'number') { }
```

### Object Type Checks

**Before:**

```javascript theme={null}
const util = require('node:util');

if (util.isDate(value)) { }
if (util.isRegExp(value)) { }
if (util.isBuffer(value)) { }
```

**After:**

```javascript theme={null}
if (value instanceof Date) { }
if (value instanceof RegExp) { }
if (Buffer.isBuffer(value)) { }
```

### Null/Undefined Checks

**Before:**

```javascript theme={null}
const util = require('node:util');

if (util.isNull(value)) { }
if (util.isUndefined(value)) { }
if (util.isNullOrUndefined(value)) { }
```

**After:**

```javascript theme={null}
if (value === null) { }
if (typeof value === 'undefined') { }
if (value === null || value === undefined) { }
```

## Usage

Run this codemod on your project:

```bash theme={null}
npx codemod node/userland/util-is
```

<Tip>
  Modern JavaScript provides native type-checking mechanisms that are more performant and widely understood. These standard approaches are preferred over Node.js-specific utilities.
</Tip>

## Related Deprecations

* [DEP0044: util.isArray()](https://nodejs.org/docs/latest/api/deprecations.html#DEP0044)
* [DEP0045: util.isBoolean()](https://nodejs.org/docs/latest/api/deprecations.html#dep0045-utilisboolean)
* [DEP0046: util.isBuffer()](https://nodejs.org/docs/latest/api/deprecations.html#dep0046-utilisbuffer)
* [DEP0047: util.isDate()](https://nodejs.org/docs/latest/api/deprecations.html#dep0047-utilisdate)
* [DEP0048: util.isError()](https://nodejs.org/docs/latest/api/deprecations.html#dep0048-utiliserror)
* [DEP0049: util.isFunction()](https://nodejs.org/docs/latest/api/deprecations.html#dep0049-utilisfunction)
* [DEP0050: util.isNull()](https://nodejs.org/docs/latest/api/deprecations.html#dep0050-utilisnull)
* [DEP0051: util.isNullOrUndefined()](https://nodejs.org/docs/latest/api/deprecations.html#dep0051-utilisnullorundefined)
* [DEP0052: util.isNumber()](https://nodejs.org/docs/latest/api/deprecations.html#dep0052-utilisnumber)
* [DEP0053: util.isObject()](https://nodejs.org/docs/latest/api/deprecations.html#dep0053-utilisobject)
* [DEP0054: util.isPrimitive()](https://nodejs.org/docs/latest/api/deprecations.html#dep0054-utilisprimitive)
* [DEP0055: util.isRegExp()](https://nodejs.org/docs/latest/api/deprecations.html#dep0055-utilisregexp)
* [DEP0056: util.isString()](https://nodejs.org/docs/latest/api/deprecations.html#dep0056-utilisstring)
* [DEP0057: util.isSymbol()](https://nodejs.org/docs/latest/api/deprecations.html#dep0057-utilissymbol)
* [DEP0058: util.isUndefined()](https://nodejs.org/docs/latest/api/deprecations.html#dep0058-utilisundefined)