hasOwnProperty vs in

const person = {
    name: 'Foo',
};

'name' in person; // true
person.hasOwnProperty('name'); // true

#Differences

1. For inherited properties, `in` will return `true`. `hasOwnProperty`, as the name implies, will check if a property is owned by itself, and ignores the inherited properties.
   Let's reuse the person object from the previous example. Since it's a JavaScript object which has built-in properties such as `constructor`, `__proto__`, the following check return true:
   js

   'constructor' in person; // true
   '__proto__' in person; // true
   'toString' in person; // true

   While `hasOwnProperty` returns `false` when checking against these properties and methods:
   js

   person.hasOwnProperty('constructor'); // false
   person.hasOwnProperty('__proto__'); // false
   person.hasOwnProperty('toString'); // false

2. For the `get` and `set` methods of a class, `hasOwnProperty` also returns `false`.
   For example, we have a simple class representing triangles:
   js

   class Triangle {
       get vertices() {
           return 3;
       }
   }
   
   // Create new instance
   const triangle = new Triangle();

   Despite the fact that `vertices` is the property of `triangle`:
   js

   triangle.vertices; // 3
   'vertices' in triangle; // true

   `hasOwnProperty` still ignores it:
   js

   triangle.hasOwnProperty('vertices'); // false

#Good practice

#See also

• Object vs Map