Chapter 4: Presentation Control

Welcome to the fourth chapter of the mock-limits tutorial!

In the previous chapter, State Evaluation, we learned how to use the isEnabled() function. We created a "Master Switch" that safely cuts the power to our unfinished features, ensuring that even if a user tries to use them, the code won't crash.

However, we are left with a User Experience (UX) problem. We have a button that doesn't crash... but it also doesn't work. It just sits there.

The Motivation: The "Broken Button" Problem

The Central Use Case: Imagine you are building an "Admin Dashboard." You have created a placeholder for a "Delete All Users" button.

Using what we learned in Chapter 3, you have disabled the logic. When you click the button, nothing happens.

1. The Good News: The database is safe.
2. The Bad News: The user is confused. They click the button. Nothing happens. They click it harder. Still nothing. They assume your website is broken and send a support ticket.

We need a way to tell the User Interface (UI) to hide this button entirely until the logic is truly ready. We need Presentation Control.

What is Presentation Control?

In mock-limits, Presentation Control is handled by the isHidden property.

Think of your computer's file system. There are thousands of system files in your folders that handle configuration, but you never see them. They have a special "Hidden" attribute.

• The file exists on the disk.
• The operating system knows it is there.
• But the user is not shown the file.

The isHidden property works the same way. It tells your dashboard or menu system: "I exist in the code, but I am irrelevant to the end-user right now. Do not draw me."

How to use Presentation Control

Let's look at how to use this property to clean up our User Interface.

The Code

In your UI code (for example, when building a menu list), you should check this property before drawing the item.

// Assume 'deleteLimit' is our mock object
const deleteLimit = require('./index');

// Check visibility before rendering
if (deleteLimit.isHidden) {
  // Option A: Do nothing (Render nothing)
  return null;
} else {
  // Option B: Render the button
  renderDeleteButton();
}

Explanation:

1. We access deleteLimit.isHidden. This is a simple boolean (true/false), not a function.
2. If it is true, we return null. In most UI frameworks (like React or Vue), returning null means "draw nothing here."
3. The button essentially vanishes from the screen.

Example Outcome

Input: deleteLimit.isHidden is true.

Output: The "Delete All Users" button does not appear on the dashboard. The user doesn't know the feature is even being developed, so they cannot be confused by a non-functional button.

Under the Hood: Internal Implementation

How does the mock-limits library define this internally?

When the UI layer is deciding what to put on the screen, it acts like a bouncer at a club. It checks the ID of every feature. If the feature is marked "Hidden," it isn't allowed on the visual stage.

Here is the flow of the Presentation Control:

The Source Code

Let's look at our trusty index.js file one last time to see the default setting.

// --- File: index.js ---

export default { 
  isEnabled: () => false, 
  
  // Presentation Control defaults to TRUE
  isHidden: true, 
  
  name: 'stub' 
};

Why is the default true?

In software development, we prefer "Safe Defaults."

• Mocks usually represent code that isn't written yet.
• Code that isn't written shouldn't be used or seen.

By defaulting isHidden to true, the library ensures that your work-in-progress features remain invisible "Ghost" features until you explicitly decide to reveal them by changing this value to false.

Conclusion

In this chapter, you learned about Presentation Control.

You learned that the isHidden property acts like an invisibility cloak. It allows you to keep code in your project without cluttering the user interface with broken or unfinished buttons.

Tutorial Wrap-up

Congratulations! You have completed the mock-limits beginner tutorial. Let's review what we built:

1. Mock Definition: We created a structural placeholder to prevent crashes.
2. Identity Management: We gave the mock a name so we can identify it in logs.
3. State Evaluation: We used isEnabled() to safely disable the logic.
4. Presentation Control: We used isHidden to clean up the UI.

You now possess a safe, robust object that you can use as a "Crash Test Dummy" for any missing feature in your application!

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