What is the purpose of guards in programming and in what situations is their use justified?

Guards in programming are constructs or functions that check certain conditions before executing the main code. Their purpose is to ensure safety, correctness, and control the flow of execution, preventing operations under inappropriate conditions.

In Node.js, guards are often used to check access rights, validate data, or verify the state before executing a request or function. For example, in web applications, guards can check whether a user is authorized before granting access to a specific resource.

Using guards is justified when it is necessary to:

• Protect the application from incorrect or malicious data.
• Control access to resources.
• Prevent code execution when conditions are not met.

An example of a simple guard in Node.js:

function isUserAdmin(user) {
  return user && user.role === 'admin';
}

function performAdminTask(user) {
  if (!isUserAdmin(user)) {
    throw new Error('Access denied');
  }
  // perform the task
}