Code recipe: Check if a JavaScript Object is empty with examples

Code snippets to help you check whether a JavaScript Object is empty or not

Posted on February 15, 2021


If you don’t want to know the explanations, here’s the code snippet to help you check whether a JavaScript Objectis empty or not:

let emptyObj = {};

if (Object.keys(emptyObj).length === 0 && emptyObj.constructor === Object) {
  console.log("Object is empty");
}

Read on to learn how and why it works.

To check whether a JavaScript Object is empty or not, you can check whether the Object variable has enumerable key names or not by using the Object.keys() method.

When you have no defined property names, the Object.keys() method will return an empty Array as follows:

let emptyObj = {};

console.log(Object.keys(emptyObj)); // Array []

let user = {
  name: "Nathan",
  age: 29,
};

console.log(Object.keys(user)); // Array ["name", "age"]

With this method, you can simply check the length of the keys array and know that the Object is empty when the length is 0:

let emptyObj = {};

if (Object.keys(emptyObj).length === 0) {
  console.log("The object is empty");
}

But be careful because JavaScript also has built-in constructors that allows you to create an Object version of primitive data types. For example, you can create a String Object like this:

let userObj = new String();

In total, JavaScript has 8 built-in constructors:

new Object(); // Object object
new String(); // String object
new Number(); // Number object
new Boolean(); // Boolean object
new Array(); // Array object
new RegExp(); // RegExp object
new Function(); // Function object
new Date(); // Date object

To check whether your Object is really an Object type, you can check whether the constructor property equals to Object.

Here’s the example:

let emptyObj = {};
console.log(emptyObj.constructor === Object); // true

let emptyStr = new String();
console.log(emptyStr.constructor === String); // true
console.log(emptyStr.constructor === Object); // false

let emptyNum = new Number();
console.log(emptyNum.constructor === Number); // true
console.log(emptyNum.constructor === Object); // false

Now you can combine both expressions to check whether an Object variable is really an Object and is empty:

let emptyObj = {};

if (Object.keys(emptyObj).length === 0 && emptyObj.constructor === Object) {
  console.log("Object is empty");
} else {
  console.log("Object is not empty");
}

Checking empty object before ES5

The Object.keys() method is only available for JavaScript version ES5 (2009) or above, so if you need to support older browsers like Internet Explorer, you can use the JSON.stringify() method and see if it returns an empty object.

Here’s an example:

let emptyObj = {};

if (JSON.stringify(emptyObj) === "{}") {
  console.log("Object is empty");
}

It’s considered a hack, but it actually works 😉

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