Clean Code in JavaScript

The instanceof operator

The instanceof operator in JavaScript allows you to detect whether an object is an instance of a constructor:

const component = new Component();component instanceof Component; 

This operation will climb the [[Prototype]] chain of its left-side operand looking for a specific constructor function. It will then check whether this constructor is equal to the right-side operand.

Since it climbs the [[Prototype]] chain, it can work safely with multiple inheritances:

class Super {}class Child extends Super {}new Super() instanceof Super; // => truenew Child() instanceof Child; // => truenew Child() instanceof Super; // => true

If the right-side operand is not a function (that is, is not callable as a constructor), then