JavaScript Errors: Bad new optional

JavaScript Errors: Bad new optional

When discussing JavaScript, one of the main errors that developers may encounter is a different type of error that occurs during code execution. One of these errors that could arise in the process of creating objects with the keyword new is the Bad new optional error. This error generally means that you are attempting to call a class or constructor that is not correctly defined. To resolve this issue, it is crucial to ensure that the function you are trying to instantiate with new is defined properly and indeed returns an object. This point is especially true for functions defined as Arrow Function; they cannot be used as constructors.

This error might occur due to an improper definition of the function or the absence of the class in question. To fix this issue, it is important to ensure that the function you are utilizing with new is appropriately defined and returns an object. This should be particularly kept in mind for functions defined as Arrow Functions, as they cannot be used as constructors.

To avoid this error, instead of using new, you can utilize other methods to create objects. For example, you might use Object.create or a regular function instead of an Arrow Function to create constructors. This approach will ensure that your code’s structure is better and avoid issues such as Bad new optional.

Below are some examples and common ways to avoid this error. We will begin with a simple example that demonstrates how a simple object can be defined using a constructor function and see how we can prevent using a faulty new.

function Person(name) {
    this.name = name;
}

const john = new Person('John');
console.log(john.name); // Output: John

// Now if we want to use an Arrow Function:
const PersonArrow = (name) => {
    this.name = name;
};

const jane = new PersonArrow('Jane'); // Here the Bad new optional error occurs!

Code Explanation

• function Person(name) { ... } This is a function called Person that takes one parameter called name and assigns it to the object.


• const john = new Person('John'); Here, using the keyword new, we create a new object named john from the Person constructor.


• console.log(john.name); // Output: John This line outputs the name john in the console.


• const PersonArrow = (name) => { ... } Here, we define an Arrow Function called PersonArrow that is similar to the previous constructor.


• const jane = new PersonArrow('Jane'); This code attempts to use new to create a new object, which results in the Bad new optional error.