If you have encountered the error message “throw new Error – ‘new’ expression, whose target lacks a construct signature” while using TypeScript, don’t worry, you’re not alone. This error typically occurs when you try to instantiate an object using the ‘new’ keyword, but the target object doesn’t have a constructor signature.

Understanding the Error

Before we dive into the solutions, let’s understand the error message in more detail. The error message indicates that the object you are trying to create an instance of doesn’t have a valid constructor signature. In TypeScript, a constructor signature is defined using the ‘new’ keyword followed by the object’s name and its parameter types.

Possible Solutions

There are a few different solutions to resolve this error. Let’s explore each one:

Solution 1: Add a Constructor Signature

The first solution is to add a constructor signature to the target object. This can be done by defining a constructor function with the required parameters. Here’s an example:

class MyClass {
  constructor(param1: string, param2: number) {
    // Constructor logic here
  }
}

const myInstance = new MyClass("example", 123);

In this example, we define a class called ‘MyClass’ with a constructor that takes two parameters: a string and a number. Now, when we create an instance of ‘MyClass’ using the ‘new’ keyword, we provide the required arguments.

Solution 2: Use Type Assertions

If you don’t have control over the target object’s definition or you’re working with a third-party library, you can use type assertions to bypass the error. Type assertions allow you to explicitly tell the TypeScript compiler the type of an expression. Here’s an example:

const myInstance = new (MyClass as any)("example", 123);

In this example, we use the ‘as’ keyword to assert the type of ‘MyClass’ as ‘any’. This tells the compiler to treat ‘MyClass’ as any type, allowing us to create an instance without a constructor signature.

Solution 3: Use Object.create

Another solution is to use the ‘Object.create’ method to create an instance of the target object. This method allows you to create an object with a specified prototype. Here’s an example:

const myInstance = Object.create(MyClass.prototype);
myInstance.constructor("example", 123);

In this example, we use ‘Object.create’ to create a new object with ‘MyClass.prototype’ as its prototype. Then, we call the constructor function on the new instance with the required arguments.

Conclusion

The “throw new Error – ‘new’ expression, whose target lacks a construct signature” error can be resolved by adding a constructor signature, using type assertions, or using ‘Object.create’. Choose the solution that best fits your specific scenario and enjoy error-free TypeScript coding!