isObject

Determines whether a value is an object (excluding null, primitives, and functions). Provides reliable object detection by checking for non-null object types, distinguishing true objects from primitives and functions while correctly handling the JavaScript quirk where typeof null === 'object'.

Signature

const isObject: (value?: unknown) => value is object

Parameters

Name	Type	Description
value	-	Value to test for object type

Returns

Type-safe boolean indicating whether the value is an object

Examples

Basic object detection

import { isObject } from '@winglet/common-utils';

console.log(isObject({})); // true
console.log(isObject({ name: 'John' })); // true
console.log(isObject([1, 2, 3])); // true (arrays are objects)
console.log(isObject(new Date())); // true
console.log(isObject(/regex/)); // true
console.log(isObject(new Map())); // true
console.log(isObject(new Set())); // true
console.log(isObject(Object.create(null))); // true

// These return false
console.log(isObject(null)); // false (important distinction)
console.log(isObject(() => {})); // false (functions are excluded)
console.log(isObject(function() {})); // false (functions are excluded)
console.log(isObject('string')); // false
console.log(isObject(42)); // false
console.log(isObject(true)); // false
console.log(isObject(undefined)); // false
console.log(isObject(Symbol('test'))); // false

Object processing with type safety

function processData(input: unknown) {
  if (isObject(input)) {
    // TypeScript knows input is object (but not function)
    console.log('Processing object:', Object.keys(input));

    // Safe to use object methods
    if ('toString' in input) {
      console.log('String representation:', input.toString());
    }
  } else {
    console.log('Not an object:', typeof input, input);
  }
}

API response validation

interface ApiResponse {
  data: unknown;
  status: number;
  message: string;
}

function validateApiResponse(response: unknown): response is ApiResponse {
  return isObject(response) &&
         'data' in response &&
         'status' in response &&
         'message' in response;
}

// Usage
fetch('/api/data')
  .then(r => r.json())
  .then(data => {
    if (validateApiResponse(data)) {
      console.log('Valid response:', data.status);
    }
  });

Playground

import { isObject } from '@winglet/common-utils';

console.log(isObject({})); // true
console.log(isObject({ name: 'John' })); // true
console.log(isObject([1, 2, 3])); // true (arrays are objects)
console.log(isObject(new Date())); // true
console.log(isObject(/regex/)); // true
console.log(isObject(new Map())); // true
console.log(isObject(new Set())); // true
console.log(isObject(Object.create(null))); // true

// These return false
console.log(isObject(null)); // false (important distinction)
console.log(isObject(() => {})); // false (functions are excluded)
console.log(isObject(function() {})); // false (functions are excluded)
console.log(isObject('string')); // false
console.log(isObject(42)); // false
console.log(isObject(true)); // false
console.log(isObject(undefined)); // false
console.log(isObject(Symbol('test'))); // false

Notes

Important Notes:

• Returns true for arrays, dates, regexes, maps, sets, and other object types
• Returns false for null (unlike raw typeof check)
• Returns false for all primitive types
• Returns false for functions (unlike raw typeof check)
• Does not distinguish between plain objects and instances

Use Cases:

• Input validation for object-like data (excluding functions)
• Type guards before property access
• API response validation
• Generic object processing functions

For more specific object type checking, consider:

• isPlainObject() for plain data objects
• isArray() for arrays specifically
• isFunction() for functions specifically
• instanceof for specific class instances