ℹ️ This repository is part of my Refactoring catalog based on Fowler's book with the same title. Please see kaiosilveira/refactoring for more details.

---

Remove dead code

Before	After
if (false) { doSomethingThatUsedToMatter(); }	// block proposefully left blank to represent nothingness

Borrowing from the biology world, "evolution" is better seen as a series of adaptations with modifications, with these modifications always focused on optimizing fitness. The side-effects of these modifications, though, are vestigial organs. Codebases also evolve towards better fitness levels, and their equivalent of vestigial organs is dead code: code that doesn't do anything anymore but used to matter at some point in time.

Working example

Since this refactoring is all about deleting unused code, the book doesn't provide any concrete example, just a dummy function that represents something that used to matter, but doesn't do it anymore.

Test suite

By the same token, no test suite was needed.

Steps

The steps are straightforward. Once we've identified the unused code, we can go and remove it:

diff --git a/src/index.js b/src/index.js
@@ -3,6 +3,5 @@ export function doSomethingThatUsedToMatter() {
 }

 export function doSomething() {
-  if (false) doSomethingThatUsedToMatter();
   return 2;
 }

Additionally, if the underlying scope of the removed code block is also not being used, we can proceed with its deletion as well:

diff --git a/src/index.js b/src/index.js
@@ -1,7 +1,3 @@
-export function doSomethingThatUsedToMatter() {
-  return 1;
-}
-
 export function doSomething() {
   return 2;
 }

diff --git a/src/index.test.js b/src/index.test.js
@@ -1,13 +1,7 @@
-import { doSomething, doSomethingThatUsedToMatter } from './index';
+import { doSomething } from './index';

 describe('doSomething', () => {
   it('should work', () => {
     expect(doSomething()).toEqual(2);
   });
 });
-
-describe('doSomethingThatUsedToMatter', () => {
-  it('should work', () => {
-    expect(doSomethingThatUsedToMatter()).toEqual(1);
-  });
-});

And that's it for this one!

Commit history

Below there's the commit history for the steps detailed above.

Commit SHA	Message
3d2faa6	remove unreachable code
3051d99	remove unused function

For the full commit history for this project, check the Commit History tab.