noUnsafeNegation

JavaScript (and super languages)

Summary

• Rule available since: v1.0.0
• Diagnostic Category: lint/suspicious/noUnsafeNegation
• This rule is recommended, which means is enabled by default.
• This rule has an unsafe fix.
• The default severity of this rule is error.
• Sources:
  • Same as no-unsafe-negation

How to configure

biome.json

{
  "linter": {
    "rules": {
      "suspicious": {
        "noUnsafeNegation": "error"
      }
    }
  }
}

Description

Disallow using unsafe negation.

Examples

Invalid

!1 in [1,2];

code-block.js:1:1 lint/suspicious/noUnsafeNegation  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ The negation operator is used unsafely on the left side of this binary expression.
  
  > 1 │ !1 in [1,2];
      │ ^^^^^^^^^^^
    2 │ 
  
  ℹ Unsafe fix: Wrap the expression with a parenthesis
  
    1 │ !(1·in·[1,2]);
      │  +          + 

/**test*/!/** test*/1 instanceof [1,2];

code-block.js:1:10 lint/suspicious/noUnsafeNegation  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ The negation operator is used unsafely on the left side of this binary expression.
  
  > 1 │ /**test*/!/** test*/1 instanceof [1,2];
      │          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ Unsafe fix: Wrap the expression with a parenthesis
  
    1 │ /**test*/!/**·test*/(1·instanceof·[1,2]);
      │                     +                  + 

Valid

-1 in [1,2];
~1 in [1,2];
typeof 1 in [1,2];
void 1 in [1,2];
delete 1 in [1,2];
+1 instanceof [1,2];

Related links

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• Configure the code fix
• Rule options
• Source Code
• Test Cases