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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Inline Variable

Formerly: Inline Temp

Before	After
let basePrice = anOrder.basePrice; return basePrice > 1000;	return anOrder.basePrice > 1000;

Inverse of: Extract Variable

Sometimes a variable is as clear and short as the expression it is derived from, and sometimes it gets in the way of refactoring the code surrounding it. In these cases, it is often best to delete the variable and inline the originating expression.

Working example

For this refactoring, we are going to analyze a function that returns a boolean saying whether an order is eligible for a discount. It returns true if the basePrice of the order is greater than 1000 and false otherwise. The starting code looks like this:

function isEligibleForDiscount(anOrder) {
  const basePrice = anOrder.basePrice;
  return basePrice > 1000;
}

Test suite

Two tests were added to cover this refactoring: one for when the function returns true and another for when it returns false:

describe("isEligibleForDiscount", () => {
  it("should return true if order.basePrice is greater than 1000", () => {
    const anOrder = { basePrice: 1001 };
    const isEligible = isEligibleForDiscount(anOrder);
    expect(isEligible).toEqual(true);
  });

  it("should return false if order.basePrice is less than 1000", () => {
    const anOrder = { basePrice: 999 };
    const isEligible = isEligibleForDiscount(anOrder);
    expect(isEligible).toEqual(false);
  });
});

Steps

To perform this refactoring, we first replace the variable by its originating expression:

diff --git a/index.js b/index.js
@@ -1,6 +1,6 @@
 function isEligibleForDiscount(anOrder) {
   const basePrice = anOrder.basePrice;
-  return basePrice > 1000;
+  return anOrder.basePrice > 1000;
 }

 module.exports = { isEligibleForDiscount };

And then simply remove the now unused variable:

diff --git a/index.js b/index.js
@@ -1,5 +1,4 @@
 function isEligibleForDiscount(anOrder) {
-  const basePrice = anOrder.basePrice;
   return anOrder.basePrice > 1000;
 }

And that's it!

Commit history

See below a chronology (from top to bottom) of all the refactoring steps:

Commit SHA	Message
8009aae	replace variable by originating expression
6eb1a50	remove unused variable basePrice

The full commit history can be seen in the Commit History tab.