How do I test for an empty JavaScript object?

More than meets the eye

Sometimes, textbooks don't cover real-world hiccups. An object may seem straightforward, but it's Objectception all the way down. When dealing with objects, we have to be sure they genuinely have no own enumerable properties. Object.keys() is suitable for ES5+ environments. We also do a constructor check to guard against JavaScript's practical jokes where null, arrays, and cross-realm objects are also types of objects.

Cross-realm and unusual prototypes

Some objects have seen more of the multiverse than Doctor Strange. Cross-realm objects and ones with unique prototypes need special care:

function isEmptyObject(obj) {
    if (obj == null || typeof obj !== 'object' || Object.getPrototypeOf(obj) !== Object.prototype) {
        return false;
    }
    for (const key in obj) {
        if (Object.hasOwn(obj, key)) {
            return false;
        }
    }
    return true;
}


Legacy environments, where people still remember dial-up tones, can use Object.prototype.hasOwnProperty.call(obj, key) instead of Object.hasOwn(obj, key).

What's in the box — Edge case handling

Prototype-free Objects

Living off the grid, ah? In JavaScript, you can create objects with no prototype using Object.create(null). Our 'hardened' isEmptyObject function pitched a tent here as well.

Symbolic times

Object.keys() doesn't get Symbol properties. They are like hipsters at a metal concert in ES6 and above. We can include them as such:

const isEmpty = obj => {
    return (
        Object.keys(obj).length === 0 &&
        Object.getOwnPropertySymbols(obj).length === 0 &&
        obj.constructor === Object
    );
};


Libraries in action

If you like your project frameworks thick, like a double cheeseburger, don't reinvent the wheel. Use _.isEmpty(obj) from lodash or $.isEmptyObject(obj) from jQuery. Just remember to wear a bib for the sauce.

In-depth detection

Not everything is plain JavaScript

Avoid JSON.stringify(obj) === "{}". It's slower than a snail climbing Mount Everest. It doesn't see non-enumerable properties either.

Keep performance in mind

Jared Leto won an Oscar for playing a method actor. Be like Jared. Test your methods in their actual parts. Use tools like JSBench.me for performance comparisons.

Don't play with fire: Type safety

Distinguishing between wave and particle is important in quantum physics. Similarly, JavaScript objects and other types require different treatments. Your isEmpty function needs to differentiate them else face the black hole of unexpected bugs.