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Implementing the displayErrorMessage method

This method will be a simple utility that displays messages to the end user. For simplicity, we will only use a basic alert box. In later projects, we will use so-called toast notifications instead, as it'll look better and will also provide a better user experience.

The following is the implementation:

displayErrorMessage(errorMessage: string): void { 
    if (!errorMessage) { 
        throw new Error("An error message must be provided!"); 
    } 
    alert(errorMessage); // bad for user experience but ignore this for     now 
} 

We have added a defensive check for the argument. In this case, using an exception makes sense because, if no message is passed, it is certainly due to a bug, so it should be discovered as soon as ...