How to Check if Object is Empty in JavaScript

Here's a Code Recipe to check if an object is empty or not. For newer browsers, you can use plain vanilla JS and use the new "Object.keys" 🍦 But for older browser support, you can install the Lodash library and use their "isEmpty" method 🤖

const empty = {};

/* -------------------------
  Plain JS for Newer Browser
----------------------------*/
Object.keys(empty).length === 0 && empty.constructor === Object
// true

/* -------------------------
  Lodash for Older Browser
----------------------------*/
_.isEmpty(empty)
// true

What is Vanilla JavaScript

Vanilla JavaScript is not a new framework or library. It's just regular, plain JavaScript without the use of a library like Lodash or jQuery.

A. Empty Object Check in Newer Browsers

We can use the built-in Object.keys method to check for an empty object.

const empty = {};

Object.keys(empty).length === 0 && empty.constructor === Object;

Why do we need an additional constructor check?

You may be wondering why do we need the constructor check. Well, it's to cover for the wrapper instances. In JavaScript, we have 9 built-in constructors.

new Object();

new String();
new Number();
new Boolean();
new Array();
new RegExp();
new Function();
new Date();

So we can create an empty object with new Object(). Side note: you should NEVER create an object using the constructor. It's considered bad practice, see Airbnb Style Guide and ESLint.

const obj = new Object();

Object.keys(obj).length === 0; // true

So just using the Object.keys, it does return true when the object is empty ✅. But what happens when we create a new object instance using these other constructors.

function badEmptyCheck(value) {
  return Object.keys(value).length === 0;
}

badEmptyCheck(new String());    // true 😱
badEmptyCheck(new Number());    // true 😱
badEmptyCheck(new Boolean());   // true 😱
badEmptyCheck(new Array());     // true 😱
badEmptyCheck(new RegExp());    // true 😱
badEmptyCheck(new Function());  // true 😱
badEmptyCheck(new Date());      // true 😱

Ah ya ya, we have a false positive 😱

Solving false positive with constructor check

Let's correct this by adding a constructor check.

function goodEmptyCheck(value) {
  Object.keys(value).length === 0
    && value.constructor === Object; // 👈 constructor check
}

goodEmptyCheck(new String());   // false ✅
goodEmptyCheck(new Number());   // false ✅
goodEmptyCheck(new Boolean());  // false ✅
goodEmptyCheck(new Array());    // false ✅
goodEmptyCheck(new RegExp());   // false ✅
goodEmptyCheck(new Function()); // false ✅
goodEmptyCheck(new Date());     // false ✅

Beautiful! We have covered our edge case 👍

Testing empty check on other values

Alright, let's test our method on some values and see what we get 🧪

function isEmptyObject(value) {
  return Object.keys(value).length === 0 && value.constructor === Object;
}

Looks good so far, it returns false for non-objects.

isEmptyObject(100)  // false
isEmptyObject(true) // false
isEmptyObject([])   // false

🚨But watch out! These values will throw an error.

// TypeError: Cannot covert undefined or null ot object
goodEmptyCheck(undefined)
goodEmptyCheck(null)

Improve empty check for null and undefined

If you don't want it to throw a TypeError, you can add an extra check:

let value;

value // 👈 null and undefined check
 && Object.keys(value).length === 0 && value.constructor === Object;

value = null;       // null
value = undefined;  // undefined

Perfect, no error is thrown 😁

B. Empty Object Check in Older Browsers

What if you need to support older browsers? Heck, who am I kidding! We all know when I say older browsers, I'm referring to Internet Explorer 😂 Well, we have 2 options. We can stick with vanilla or utilize a library.

Checking empty object with JavaScript

The plain vanilla way is not as concise. But it does do the job 👍

function isObjectEmpty(value) {
  return Object.prototype.toString.call(value) === "[object Object]" && JSON.stringify(value) === "{}"
}

It returns true for objects.

isObjectEmpty({});           // true ✅
isObjectEmpty(new Object()); // true ✅

Excellent, it doesn't get trick by our constructor objects 😉

isObjectEmpty(new String());   // false ✅
isObjectEmpty(new Number());   // false ✅
isObjectEmpty(new Boolean());  // false ✅
isObjectEmpty(new Array());    // false ✅
isObjectEmpty(new RegExp());   // false ✅
isObjectEmpty(new Function()); // false ✅
isObjectEmpty(new Date());     // false ✅

And we're covered for null and undefined. It will return false and not throw a TypeError.

isObjectEmpty(null);      // false
isObjectEmpty(undefined); // false

Checking empty object with external libraries

There are tons of external libraries you can use to check for empty objects. And most of them have great support for older browsers 👍

Lodash

_.isEmpty({});
// true

Underscore

_.isEmpty({});
// true

jQuery

jQuery.isEmptyObject({});
// true

Vanilla vs Libraries

The answer is it depends! I'm a huge fan of going vanilla whenever possible as I don't like the overhead of an external library. Plus for smaller apps, I'm too lazy to set up the external library 😂. But if your app already has an external library installed, then go ahead and use it. You will know your app better than anyone else. So choose what works best for your situation 👍

Conscious Decision Making

• @lexLohr: Like most things in development, it's a compromise. A good developer is aware of the available options. A great developer is also aware of their implications.

I love this mindset so much! Often, we have to make some compromises. And there's nothing wrong with that. Especially, when you work within a team, sometimes disagreement arises. But in the end, we have to make a decision. This doesn't mean we blind ourselves from other options. Quite the opposite, we do our best to seek other possible solutions and understand each implication. That's how we can make an informed decision. Maybe compromise is not the right word, I think of it as "conscious decision making" 😆

Yup, I too can coin terms, just like Gwyneth Paltrow's conscious uncoupling. Maybe I should start a tech version of Goop...but minus the jade roller and the other "interesting" products 😂

Community Input

• @lexLohr

for (var key in object) {
  if (object.hasOwnProperty(key)) {
    return false
  }
}
return true

• @amanboss_9

Object.prototype.toString.call(a) == "[object Object]" && JSON.stringify(a) == "{}"

• @kevinsar: Lodash tends to throw security exceptions in analysis tools like sonarqube and whitesource, I tend to just create my own util function and use vanilla instead.

  • @sush_keny: (Because of) prototype pollution

• @functional_js: isNotObj Gist

Resources

• MDN: Object.keys()
• w3schools: Built-in JavaScript Constructors
• Stack Overflow: Is object empty?
• Stack Overflow: How do I test for an empty JavaScript object?
• CSS Tricks: Understanding JavaScript Constructors
• JavaScript's Primitive Wrapper Objects
• Wrapper Objects
• JavaScript’s Primitive Wrapper Objects
• ESLint: Disallow Primitive Wrapper Instances
• Airbnb: no-new-object
• Lodash: isEmpty
• Underscore: isEmpty
• jQuery: isEmptyObject

Thanks for reading ❤
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