noMagicNumbers

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TypeScript and TSX

Summary

Rule available since: v2.1.0
Diagnostic Category: lint/nursery/noMagicNumbers
This rule doesn’t have a fix.
The default severity of this rule is information.
Sources:
- Same as @typescript-eslint/no-magic-numbers

Description

Reports usage of “magic numbers” — numbers used directly instead of being assigned to named constants.

Its goal is to improve code maintainability and readability by encouraging developers to extract such numbers into named constants, making their purpose explicit.

It ignores:

non-magic values (like 0, 1, 2, 10, 24, 60, and their negative or bigint forms) found anywhere, including arithmetic expressions, fn calls etc.
Array indices
Enum values
Initial values in variable or class property declarations
Default values in function parameters or destructuring patterns
Arguments to JSON.stringify and parseInt (e.g., JSON.stringify(22), parseInt("123", 8))
Operands in bitwise operations (e.g., a & 7, a | 7)
Values in JSX expressions (e.g., <div>{1}</div>)
Object property values (e.g., { tax: 0.25 })

Examples

Invalid

1
let total = price * 1.23; // Magic number for tax rate

code-block.js:1:21 lint/nursery/noMagicNumbers ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Magic number detected. Extract it to a constant with a meaningful name.
  
  > 1 │ let total = price * 1.23; // Magic number for tax rate
      │                     ^^^^
    2 │ 
  
  ℹ Code is more readable and refactoring easier when special numbers are declared as constants as it makes their meaning explicit.

Valid

1
const TAX_RATE = 1.23;
2
let total = price * TAX_RATE;

1
const TAX_RATE = 1.23 as const;
2
let total = price * TAX_RATE;

How to configure

1
{
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  "linter": {
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    "rules": {
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      "nursery": {
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        "noMagicNumbers": "error"
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      }
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    }
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  }
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}