Called on an object instance, accepts a string as argument. If the object has a property with the name contained in the string argument, and that property is enumerable, it returns true. Otherwise it returns false.

Example:

const person = { name: 'Fred' }

Object.defineProperty(person, 'age', {
  value: 87,
  enumerable: false
})

person.propertyIsEnumerable('name') //true
person.propertyIsEnumerable('age') //false