References

Beginner-friendly references for web development, with live, editable examples.

The JavaScript Object.hasOwn() method

Method JavaScript All modern browsers Updated
Quick answer

The Object.hasOwn() method returns true if an object has a property as its own (not inherited from the prototype). Object.hasOwn(obj, "name"). It's the modern, safer replacement for obj.hasOwnProperty("name"), which can break on objects without a prototype or with a shadowed method.

Overview

Object.hasOwn() checks whether a property belongs to an object directly, rather than being inherited through the prototype chain. Object.hasOwn(user, "email") is true only if user has its own email property. This matters when you need to distinguish an object's real data from inherited methods, or to safely check for a key that might hold a falsy value like 0 or "" (where if (obj.key) would be misleading).

It's the modern replacement for obj.hasOwnProperty("key"), which has two long-standing pitfalls. An object created with Object.create(null) has no prototype, so it doesn't have a hasOwnProperty method and calling it throws. And an object could define its own property named hasOwnProperty, shadowing the real one. Object.hasOwn() sidesteps both by being a static method you call on the Object constructor.

It complements the in operator, which is different: "key" in obj is true for inherited properties too. Use in when inherited members count, and Object.hasOwn() when you specifically want own properties — for example when iterating with for...in, which visits inherited keys.

Syntax

Object.hasOwn(obj, propertyKey)

Object.hasOwn({ a: 1 }, "a")   // true
Object.hasOwn({ a: 1 }, "b")   // false
Object.hasOwn({ a: 1 }, "toString") // false (inherited)

Parameters

The Object.hasOwn() method accepts the following parameters.

Parameter Description
obj The object to test.
propertyKey The property name (or symbol) to check for as an own property.

Example

Live example 
<pre id="out" style="font:15px ui-monospace,monospace"></pre>
<script>
  const user = { name: 'Ada', score: 0 };

  document.getElementById('out').textContent =
    'has name?  ' + Object.hasOwn(user, 'name') + '\n' +
    'has score? ' + Object.hasOwn(user, 'score') + '\n' +
    'has email? ' + Object.hasOwn(user, 'email');
  // true / true / false
</script>

Best practices

  • Use Object.hasOwn(obj, key) instead of obj.hasOwnProperty(key) — it's safer.
  • Reach for it to check keys that might hold falsy values, where if (obj.key) is unreliable.
  • Use it to skip inherited keys inside a for...in loop.
  • Use the in operator instead when inherited properties should also count.

Frequently asked questions

What does Object.hasOwn() do?
It returns true if an object has the given property as its own (not inherited), and false otherwise.
What is the difference between Object.hasOwn() and hasOwnProperty()?
They do the same check, but Object.hasOwn() is a static method that works even on prototype-less objects and can't be shadowed, so it's the safer modern choice.
What is the difference between Object.hasOwn() and the in operator?
Object.hasOwn() only counts own properties; "key" in obj is also true for inherited ones.
Why use Object.hasOwn() instead of if (obj.key)?
Because if (obj.key) is false when the value is falsy (0, "", false) even if the key exists. Object.hasOwn() checks existence, not truthiness.
Object.fromEntries() Object.keys()