You’re watching a Nollywood movie where the main character is making all the wrong choices. Instead of solving the problem, every decision makes life harder. That’s exactly what anti-patterns are in programming.

An anti-pattern is a common coding practice that looks like a solution but actually causes more harm than good. Unlike a simple bug, an anti-pattern is intentional — it’s code that “works” but leads to confusion, errors, or maintenance nightmares later.

In this lesson, we’ll look at what anti-patterns are, why they’re dangerous, and examples of common ones in JavaScript.

🌍 What are Anti-Patterns?

  • Patterns are best practices — proven ways of solving problems (like using forEach to loop through arrays).
  • Anti-patterns are the opposite — bad habits that look useful at first but create long-term problems.

👉 They usually arise because developers want a quick fix or don’t know a better alternative.

⚠️ Why Avoid Anti-Patterns?

  1. They make code harder to read.
  2. They introduce hidden bugs.
  3. They increase maintenance costs.
  4. They create performance issues.
  5. They confuse new team members (because the code looks weird or inconsistent).

🔑 Common JavaScript Anti-Patterns

1. Using Global Variables Everywhere

name = "Ada";  // Implicit global

This works, but it pollutes the global scope. Any script can accidentally overwrite name.

✅ Better: Always declare variables with let, const, or var.

let name = "Ada";

2. Modifying Built-in Objects

Array.prototype.myMethod = function() {
  return "dangerous!";
};

Looks clever, but this can break other libraries relying on Array.

✅ Better: Use utility functions or standalone helpers instead of changing built-ins.

3. Using eval()

let result = eval("2 + 3 * 5");

It works, but eval is insecure, slow, and hard to debug.

✅ Better: Use direct operations or safe alternatives like JSON.parse() or libraries for dynamic evaluation.

4. With Statement

with (obj) {
  console.log(name);
}

This makes code ambiguous — name could come from obj or somewhere else.

✅ Better: Access properties directly:

console.log(obj.name);

5. Magic Numbers & Strings

if (userRole === 7) { /* ... */ }

What does 7 mean? Without context, future developers are lost.

✅ Better: Use named constants.

const ADMIN_ROLE = 7;
if (userRole === ADMIN_ROLE) { /* ... */ }

6. Callback Hell

getData(function(a) {
  process(a, function(b) {
    save(b, function(c) {
      notify(c, function() {
        console.log("done");
      });
    });
  });
});

This “pyramid of doom” is messy and unreadable.

✅ Better: Use Promises or async/await.

async function main() {
  const a = await getData();
  const b = await process(a);
  const c = await save(b);
  await notify(c);
  console.log("done");
}

7. Copy-Paste Programming

Repeating the same logic in multiple places.

✅ Better: Create reusable functions or modules.

🎯 The Mindset Shift

Avoiding anti-patterns isn’t just about writing “fancy” code. It’s about writing clean, maintainable, and predictable code.

Think of it like driving in Lagos traffic:

  • You can drive against one-way and reach your destination faster (a quick hack).
  • But long term, it causes chaos, accidents, and penalties (anti-patterns).

Good patterns are like following road rules — everyone gets home safer, and the journey is smoother.

✅ Summary

  • Anti-patterns = bad coding practices that seem helpful but cause long-term harm.
  • Common ones include: global variables, modifying built-ins, using eval(), with statements, magic numbers, callback hell, and copy-paste coding.
  • The solution is to use modern, safe, and clean alternatives.
  • Avoiding anti-patterns makes your code more readable, maintainable, and secure.

📝 Review – Fill in the Gaps

  1. An anti-pattern is a common but __ solution that causes long-term problems.
  2. Declaring variables without let or const creates unwanted __ variables.
  3. Changing Array.prototype is considered an anti-pattern because it can break other __.
  4. The eval() function is dangerous because it’s slow and a __ risk.
  5. The with statement makes code __ and confusing.
  6. Using numbers like 7 to represent roles is called using __ numbers.
  7. Callback hell is also called the pyramid of __.
  8. A better alternative to callback hell is using __ or async/await.
  9. Repeating the same logic in multiple places is known as copy-____ programming.
  10. Avoiding anti-patterns makes code more clean, __, and secure.
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