Can you explain how guard mechanisms are implemented and used in programming?

Guard mechanisms in programming are used to check conditions and prevent code execution if these conditions are not met. In Node.js and JavaScript, guards are often implemented through early exits from functions or blocks when conditions are not satisfied.

For example, instead of nested if statements, you can write:

function processUser(user) {
  if (!user) return; // guard: exit if user is not present
  if (!user.isActive) return; // guard: exit if user is inactive

  // main code that runs only if conditions are met
  console.log(`Processing user ${user.name}`);
}

This approach improves readability and reduces code nesting, making the logic clearer and easier to maintain.