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.

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Substitute Algorithm

Before	After
function foundPerson(people) { for (let i = 0; i < people.length; i++) { if (people[i] === 'Don') { return 'Don'; } if (people[i] === 'John') { return 'John'; } if (people[i] === 'Kent') { return 'Kent'; } } return ''; }	function foundPerson(people) { const candidates = ['Don', 'John', 'Kent']; return people.find(p => candidates.includes(p)) || ''; }

Sometimes we try our best to improve a piece of code, but it's not enough. Some other times, we take a look at a piece of logic and identify straightaway an easier, more readable way of implementing it. This refactoring helps us in these cases.

Working example

Our working example is a foundPerson function that uses a suboptimal approach to if statements and that's not leveraging the functional aspects of Javascript. Our goal here is to make this function easier to read and potentially shorter.

Test suite

A test suite was put in place to make sure that for a given input, the output of the function remains the same. This will be critical in providing us with confidence that we haven't broken anything while performing the rewrite.

describe('foundPerson', () => {
  it('should return Don if he was found', () => {
    const people = ['Don', 'Kaio', 'Dan'];
    expect(foundPerson(people)).toEqual('Don');
  });

  it('should return John if he was found', () => {
    const people = ['Kaio', 'John', 'Dan'];
    expect(foundPerson(people)).toEqual('John');
  });

  it('should return Kent if he was found', () => {
    const people = ['Kaio', 'Dan', 'Kent'];
    expect(foundPerson(people)).toEqual('Kent');
  });

  it('should return an empty string if none of the expected people were found', () => {
    const people = ['Kaio', 'Dan', 'Enzo'];
    expect(foundPerson(people)).toEqual('');
  });
});

Steps

This is one of the shortest refactorings to document: we simply need to rewrite all the logic. Of course, in the real world, some time and/or previous knowledge is required to know how to implement certain algorithms in a more idiomatic way. This is often highly dependent on the programming language we're using and the tools, libs and frameworks we have available at the time.

diff --git a/src/index.js b/src/index.js
@@ -1,17 +1,4 @@
 export function foundPerson(people) {
-  for (let i = 0; i < people.length; i++) {
-    if (people[i] === 'Don') {
-      return 'Don';
-    }
-
-    if (people[i] === 'John') {
-      return 'John';
-    }
-
-    if (people[i] === 'Kent') {
-      return 'Kent';
-    }
-  }
-
-  return '';
+  const candidates = ['Don', 'John', 'Kent'];
+  return people.find(p => candidates.includes(p)) || '';
 }

Commit history

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

Commit SHA	Message
30d67fc	rewrite foundPerson implementation

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