This content originally appeared on DEV Community and was authored by Maxi Contieri
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
- Remove unused assignments.
- 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
More Information
Disclaimer
Code Smells are my opinion.
Credits
Photo by Evan Demicoli on Unsplash
If you have to spend effort to decipher code, you should rewrite it.
Martin Golding
This article is part of the CodeSmell Series.
This content originally appeared on DEV Community and was authored by Maxi Contieri
Maxi Contieri | Sciencx (2025-01-29T17:04:31+00:00) Code Smell 287 – Unused Local Assignment. Retrieved from https://www.scien.cx/2025/01/29/code-smell-287-unused-local-assignment/
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