What are enumerable properties in JavaScript?

Enumerable properties in JavaScript are properties of an object, that can be iterated over in the for in loop or Object.keys function.

Here's an example:

const object = {
  Hello: 'World!',
  Mary: 'Jane'

// This will output:
// Hello World!
// Mary Jane
for (const key in object) {
  console.log(key, object[key]);

// Although this object also has other, built-in,
// non-enumerable properties, such as:
console.log(object.constructor); // ƒ Object() { [native code] }
console.log(object.toString); // ƒ toString() { [native code] }