Refactoring 008 – Variables That Never Change Should Be Constants

digitado ⋅ 30 de March de 2026

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 😔

Mutability
Code Optimization

Related Code Smells 💨

https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxxii?embedable=true

https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxvi?embedable=true

https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxiv?embedable=true

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.

Tags 🏷️

Mutability

Level 🔋

[X] Beginner

Related Refactorings 🔄

https://hackernoon.com/improving-the-code-one-line-at-a-time?embedable=true

Refactor with AI 🤖

Suggested Prompt: 1. Find the scope of the variable.2. Define a constant with the same scope.3. Replace the variable