Simplest Way to Check for Empty Objects in JavaScript

Check for empty objects in JavaScript with one line

Ferenc Almasi • 🔄 2022 June 20 • 📖 2 min read

The easiest way to check if an object is empty in JavaScript is to use a combination of Object.keys and a constructor check:

  Object.keys(emptyObject).length === 0 && emptyObject.constructor === Object

// How to check if an object is empty using an if statement
const emptyObject = {};

if (Object.keys(emptyObject).length === 0 && emptyObject.constructor === Object) {
  // 👌 This means your object is empty
}

empty.js

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Object.keys returns an array of the property names based on the passed object. But why do we need the second check for the constructor?

This is because Object.keys alone will return true if you pass anything else than an object:

Object.keys(0).length    === 0; // This will return true
Object.keys([]).length   === 0; // This will return true
Object.keys(true).length === 0; // This will return true
Object.keys('').length   === 0; // This will return true

empty.js

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Even though we are not checking against an object, but other arbitrary data, the equation will return true. This is why we must check if the constructor is of type Object.

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Browser Support

While Object.keys has fairly good support, if you need to fall back to older browsers, you can use the following solution:

// Fallback for older browsers
obj.constructor === Object && JSON.stringify(obj) === '{}';

// or
Object.prototype.toString.call(obj) === '[object Object]' && JSON.stringify(obj) === '{}';

empty.js

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This solution makes use of JSON.stringify, which is used for converting objects to JSON strings.

Keep in mind that for both solutions, you will get an error if you try to use it on a null or undefined value.

Uncaught TypeError: Cannot convert undefined or null to object

To get around this, you first need to check if the variable exists:

// Prevent errors for null and undefined

const emptyObject = {};

// The first check here is used for filtering out null and undefined
if (emptyObject && Object.keys(emptyObject).length === 0 && emptyObject.constructor === Object) {
  // 👌 This means your object is empty
}

empty.js

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Or wrapping the whole thing into a function:

const isEmptyObject = object => {
  if (Object.keys) {
    return object &&
           Object.keys(object).length === 0 &&
           object.constructor === Object;
  }

  return obj.constructor === Object && JSON.stringify(obj) === '{}';
};

isEmptyObject({}); // Returns true
isEmptyObject([]); // Returns false
isEmptyObject(0);  // Returns false