Magic Numbers/Strings

Unexplained literals in code.

“Avoid constants embedded in code.” – Robert C. Martin, Steve McConnell

Signs of Use (Symptoms)

  • Numbers like 86400, 3.14159, 1000 without explanation.
  • Strings like "ADMIN", "pending" scattered throughout.

Why it is bad (Consequences)

  • Readability: What does 86400 mean?
  • Maintainability: If the value changes, you must find all occurrences.
  • Typo risk: "penidng" vs "pending".

Why it happens (Root Cause)

Faster to just type the number than to define a constant.

When it might be okay (Exceptions)

  • 0, 1 in obvious contexts (loop start, boolean).
  • Mathematical constants where names don’t add clarity.

Explanation

Problem

setTimeout(fn, 86400000). What is 86400000?

The Flaw

It’s milliseconds in a day. But reader has to calculate. And if it’s wrong, no one notices.

Real world analogy

A recipe that says “bake at 423” instead of “bake at 425°F (220°C)”. Why 423?

Refactoring Solution

  • Replace Magic Number with Symbolic Constant.

Pros and Cons (of the Antipattern)

Pros (Why people do it) Cons (The price you pay)
  • Fast typing
    		•
  • Unreadable
  • Error prone
    		•

    Comparison

    • Related Antipatterns: Uncommunicative Name.
    • Related Principles: Readability.

    Code example

    Typescript

    Bad (The Antipattern)

    Good (The Fix)

    PHP

    Good (The Fix)