Comparing the Javascript ‘hasOwn()’ method vs the ‘in’ operator

DanielDecember 16, 2022December 17, 2022

This post explores what are the differences between the in and hasOwn() in Javascript.

Even if they are both used for checking if an object has a given property, the biggest difference between these two is that in will return true for inherited properties, whereas hasown() will return false for inherited properties.

Let's seen an example:

class Human {
  name
}

class Employee extends Human {
  salary
}

const obj = new Employee()

console.log("salary" in obj) // true
console.log(Object.hasOwn(obj, "salary")) // true

console.log("name" in obj) // true
console.log(Object.hasOwn("name")) // false

A few notes:

• the hasown() method comes as a replacement for the older hasOwnProperty(). More details in this StackOverflow thread.
• the in operator works also to check if private properties are set on a Js object. Of course, this assumes that the check is done inside of the class that contains that private property.

You can find here more details about the hasown() method and here more details about the in operator.