Checking instance type with instanceOf

There are many situations, such as argument validation, where we'll want to check the class of an object. Because JavaScript is not statically typed, we can't guarantee that a function receives an argument of the correct type before the program starts, and we need to check at runtime.

In this recipe, we'll see how to use the instanceOf operator to check an object's prototype at runtime.

Getting ready

This recipe assumes you already have a workspace that allows you to create and run ES modules in your browser. If you don't, please see the first two chapters.

How to do it...

1. Open your command-line application and navigate to your workspace.
2. Create a new folder named 07-04-checking-with-instanceof.
3. Copy or create an index.html that loads and runs a main function from main.js.

4. Create a main.js with two identical classes, Rocket and InactiveRocket:

// main.js class Rocket { 
  constructor(name) { 
    this.name = name; 
  } 
} 
 
class InactiveRocket { 
  constructor...