Code Smell - Unused Local Assignment

Are you using the returned value?

TL;DR: Avoid assigning values you never use.

Problems

• Dead code
• Unclear intent
• Maintenance overhead
• Hidden complexity
• Debugging leftovers
• Bad scoping
• Commented code
• Mutability

Solutions

1. Remove unused assignments.
2. Try to avoid side effects.

Context

When you assign a value to a local variable but never use it, you create unnecessary clutter in your code.

This can confuse others and make the code harder to maintain.

Sometimes, when debugging you can assign temporal variables for better inspection.

This also happens when you assign the execution to an object property but it is harder to follow.

It is also a sign of a mutating object because if you remove the assignment, only the side effects remain.

Mutating objects can cause unexpected side effects, making it harder to track changes.

Sample Code

Wrong

function updateUserName(user, newname) {
  user.name = newname;
  return user;
}

function performMaintenance(existingUser) {
  let updatedUser = updateUserName(existingUser, "Bobby Peru");
  // Other tasks
}
// The variable updatedUser is never used

Right

function updateUserName(user, newname) {
  user.name = newname;
  // Just side effects without explicit return
}

function performMaintenance(existingUser) {
  updateUserName(existingUser, "Bobby Peru");
  // Other tasks
}

Detection

[X] Automatic

You can detect this smell using static analysis tools or code reviews that check for unused variables after assignment.

Most linters flag this as an issue.

Tags

• Bloaters

Level

[x] Beginner

Why the Bijection Is Important

It stays clean and efficient when your code accurately reflects real-world logic.

Unused assignments break this connection, making it harder to understand the intent and maintain the code.

AI Generation

AI tools seldom generate unused variable assignments when they misunderstand intent.

AI Detection

AI-assisted refactoring with clear instructions can flag unused variables and suggest removals, but it might not always understand if the return value should have been used.

Try Them!

Remember: AI Assistants make lots of mistakes

Without Proper Instructions	With Specific Instructions
ChatGPT	ChatGPT
Claude	Claude
Perplexity	Perplexity
Copilot	Copilot
Gemini	Gemini
DeepSeek	DeepSeek
Meta AI	Meta AI

Conclusion

Unused variables after mutations create noise and confusion.

Don't assign the return value if you don't need it.

If the method should return something meaningful, make sure you use it.

Relations

Code Smell 209 - Side Effects

Maxi Contieri ・ Apr 28 '23

#webdev #javascript #beginners #programming

Code Smell 176 - Changes in Essence

Maxi Contieri ・ Nov 2 '22

#webdev #javascript #beginners #programming

Code Smell 154 - Too Many Variables

Maxi Contieri ・ Jul 31 '22

#webdev #beginners #programming #tutorial

Code Smell 107 - Variables Reuse

Maxi Contieri ・ Dec 1 '21

#oop #programming #webdev #tutorial

More Information

The evil powers of mutants

Maxi Contieri ・ Dec 19 '20

#webdev #programming #mutation #oop

Disclaimer

Code Smells are my opinion.

Credits

Photo by Evan Demicoli on Unsplash

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If you have to spend effort to decipher code, you should rewrite it.

Martin Golding

Software Engineering Great Quotes

Maxi Contieri ・ Dec 28 '20

#codenewbie #programming #quotes #software

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This article is part of the CodeSmell Series.

How to Find the Stinky parts of your Code

Maxi Contieri ・ May 21 '21

#codenewbie #tutorial #codequality #beginners

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