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The in operator is pretty useful. It allows us to check if an object has a property.
This operator returns true if the first operand is a property of the object passed on the right, or a property of one of its ancestors in its prototype chain.
Otherwise it returns false.
Example:
class Car {
constructor() {
this.wheels = 4
}
}
class Fiesta extends Car {
constructor() {
super()
this.brand = 'Ford'
}
}
const myCar = new Fiesta()
'brand' in myCar //true
'wheels' in myCar //true