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Jesús Mejías Leiva for Product Hackers

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Code Smell | Magic Numbers

Hello, today we are back with the code smells refactoring series and in this case we are going to talk about code smell called Magic Numbers, this code smell can be detect when we use a number that lacks the proper semantics.


Numbers lacking semantics make calculations harder to read.


As we can see in the following example we have 2 magic numbers that are quite easy to detect since it is really complex to know what type of calculation we are performing simply by observing these values: 4.50 and 0.21

function calculateTotal(subtotal) {
  const total = subtotal + 4.50;
  return total + (total * 0.21);
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By extracting both numbers to constants and giving them semantics we can see that the code is much more readable.

const SHIPPING_FEE = 4.50;
const SALES_TAX = 0.21;

function calculateTotal(subtotal) {
  const total = subtotal + SHIPPING_FEE;
  return total + (total * SALES_TAX);
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  • Improvement the readability and maintainability of the code.
  • You will make the next person who needs to go through that part of the code very happy 😋 jiji

Thanks for reading me 😊

Top comments (2)

mcsee profile image
Maxi Contieri


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Jesús Mejías Leiva

Thanks for you comment Maxi 😊