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The JavaScript Interview Handbook: 100+ Interview Questions

Solution Review: Inheritance Check

Explore how to validate inheritance correctly in JavaScript by using instanceof and proper class syntax. Understand why inheritance may fail without the extends keyword and how constructor implementation affects object behavior. This lesson helps you identify and fix common inheritance issues in JavaScript.

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Solution

Javascript (babel-node)
class Vehicle {
  constructor() {
    var speed = "100";
    var model = "Tesla";
  }
}
class Car {
  constructor() {
    var speed = "100";
    var model = "Tesla";
  }
}
var car = new Car();
function check() {
  if (!(car instanceof Vehicle)) {
    console.log("Inheritance not implemented");
  } else {
    console.log("Good job");
  }
}
check();
...