noExtraBooleanCast (JavaScript)

Language JavaScript (and super languages)

Summary

• Rule available since: v1.0.0
• Diagnostic Category: lint/complexity/noExtraBooleanCast
• This rule is recommended, meaning it is enabled by default.
• This rule has a safe fix.
• The default severity of this rule is information.
• Sources:
  • Same as no-extra-boolean-cast

How to configure

biome.json

{
  "linter": {
    "rules": {
      "complexity": {
        "noExtraBooleanCast": "error"
      }
    }
  }
}

Description

Disallow unnecessary boolean casts

Examples

Invalid

if (!Boolean(foo)) {
}

code-block.js:1:6 lint/complexity/noExtraBooleanCast  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Avoid redundant `Boolean` call
  
  > 1 │ if (!Boolean(foo)) {
      │      ^^^^^^^^^^^^
    2 │ }
    3 │ 
  
  ℹ It is not necessary to use `Boolean` call when a value will already be coerced to a boolean.
  
  ℹ Safe fix: Remove redundant `Boolean` call
  
    1 │ if·(!Boolean(foo))·{
      │      --------   -   

while (!!foo) {}

code-block.js:1:8 lint/complexity/noExtraBooleanCast  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Avoid redundant double-negation.
  
  > 1 │ while (!!foo) {}
      │        ^^^^^
    2 │ 
  
  ℹ It is not necessary to use double-negation when a value will already be coerced to a boolean.
  
  ℹ Safe fix: Remove redundant double-negation
  
    1 │ while·(!!foo)·{}
      │        --       

let x = 1;
do {
1 + 1;
} while (Boolean(x));

code-block.js:4:10 lint/complexity/noExtraBooleanCast  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Avoid redundant `Boolean` call
  
    2 │ do {
    3 │ 1 + 1;
  > 4 │ } while (Boolean(x));
      │          ^^^^^^^^^^
    5 │ 
  
  ℹ It is not necessary to use `Boolean` call when a value will already be coerced to a boolean.
  
  ℹ Safe fix: Remove redundant `Boolean` call
  
    4 │ }·while·(Boolean(x));
      │          -------- -  

for (; !!foo; ) {}

code-block.js:1:8 lint/complexity/noExtraBooleanCast  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Avoid redundant double-negation.
  
  > 1 │ for (; !!foo; ) {}
      │        ^^^^^
    2 │ 
  
  ℹ It is not necessary to use double-negation when a value will already be coerced to a boolean.
  
  ℹ Safe fix: Remove redundant double-negation
  
    1 │ for·(;·!!foo;·)·{}
      │        --         

new Boolean(!!x);

code-block.js:1:13 lint/complexity/noExtraBooleanCast  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Avoid redundant double-negation.
  
  > 1 │ new Boolean(!!x);
      │             ^^^
    2 │ 
  
  ℹ It is not necessary to use double-negation when a value will already be coerced to a boolean.
  
  ℹ Safe fix: Remove redundant double-negation
  
    1 │ new·Boolean(!!x);
      │             --   

Valid

Boolean(!x);
!x;
!!x;

Related links

• Disable a rule
• Configure the code fix
• Rule options
• Source Code (Edit this Page)
• Test Cases
• Try in the playground