If I see a Variable that doesn't change. I call that variable a constant
TL;DR: Be explicit on what mutates and what doesn't.
Problems Addressed
https://maximilianocontieri.com/code-smell-158-variables-not-variable
https://maximilianocontieri.com/code-smell-127-mutable-constants
https://maximilianocontieri.com/code-smell-116-variables-declared-with-var
Context
Variables that never change their value are not really variables.
They’re constants pretending to be mutable state.
When we declare something as a variable, we tell the reader (and the compiler) to expect change.
If that change never happens, we’re sending misleading signals about what the code actually does.
Converting these to constants shrinks the state space a developer must track.
A constant signals that a value won’t change, preventing accidental reassignments and letting the compiler optimize better.
It’s honest: if something shouldn’t mutate, don’t let it.
Steps
Find the scope of the variable
Define a constant with the same scope
Replace the variable
Sample Code
Before
let lightSpeed = 300000;
var gravity = 9.8;
// 1. Find the scope of the variable
// 2. Define a constant with the same scope
// 3. Replace the variable
After
const lightSpeed = 300000;
const gravity = 9.8;
// 1. Find the scope of the variable
// 2. Define a constant with the same scope
// 3. Replace the variable
// If the object is compound,
// we might need Object.freeze(gravity);
Type
[X] Automatic
IDEs can check if a variable is written but never updated.
Safety ️
This is a safe refactoring.
Why is the Code Better? ✨
Code is more compact and declares intent clearly.
Take it further with language-specific operators like const, final, or let.
The scope becomes obvious at a glance.
How Does it Improve the Bijection? ️
This refactoring improves bijection by making it clear what mutates and what doesn't.
In the real world, most values don't change. They're constants.
Declaring them as variables creates coupling between what we're thinking and how we wrote it.
Constants remove that gap and align the code with the actual domain.
Level
[X] Beginner
https://maximilianocontieri.com/refactoring-003-extract-constant
Refactor with AI
Suggested Prompt: 1. Find the scope of the variable.2. Define a constant with the same scope.3. Replace the variable
See also
https://coderlegion.com/6742/the-evil-power-of-mutants
This article is part of the Refactoring Series
https://maximilianocontieri.com/how-to-improve-your-code-with-easy-refactorings