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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Replace Inline Code with Function Call

Before	After
let appliesToMass = false; for (const s of states) { if (s === 'MA') appliesToMass = true; }	appliesToMass = states.includes('MA');

Sometimes (and especially in large codebases) it's common for us to find code that is doing essentially the same sequence of computations that we have already encapsulated in a nearby function. In these cases, we can simply replace this block of computation with a function call.

Working example

Our working example is a pretty simple one: a function that checks whether or not we have "MA" as one of the states in a list of states. Our goal is to leverage the language support for this kind of operation, so we can make the code more idiomatic.

Test suite

Our test suite is straightforward: we test both possibilities for the appliesToMass function: either returning true or false:

describe('appliesToMass', () => {
  it('should return true if Massachussets is in the list of states', () => {
    expect(appliesToMass(['MA', 'NH', 'ME'])).toBe(true);
  });

  it('should return true if Massachussets is not in the list of states', () => {
    expect(appliesToMass(['NH', 'ME'])).toBe(false);
  });
});

Steps

This is a quick one: we just need to replace the existing for loop with Array.includes:

diff --git a/src/index.js b/src/index.js
@@ -1,9 +1,3 @@
 export function appliesToMass(states) {
-  let appliesToMass = false;
-
-  for (const s of states) {
-    if (s === 'MA') appliesToMass = true;
-  }
-
-  return appliesToMass;
+  return states.includes('MA');
 }

And that's it!

Commit history

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

Commit SHA	Message
fc4baf6	replace for loop with Array.includes