noUnreadableIife (JavaScript)

Language JavaScript (and super languages)

Summary

Rule available since: v2.6.4
Diagnostic Category: lint/nursery/noUnreadableIife
This rule has an unsafe fix.
The default severity of this rule is information.
Sources:
- Same as unicorn/no-unreadable-iife

How to configure

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{
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  "linter": {
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    "rules": {
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      "nursery": {
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        "noUnreadableIife": "error"
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      }
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    }
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  }
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}

Description

Disallow immediately called arrow functions whose body is wrapped in parentheses.

An immediately invoked function expression, or IIFE, is a function that is called right where it is defined, such as (() => value)().

When the body of such an arrow function is also wrapped in parentheses, the code contains several nested pairs of parentheses. This makes the function look like a grouped expression and hides where the function body starts and ends.

Examples

Invalid

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const foo = (bar => (bar ? bar.baz : baz))(getBar());

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

  ℹ This immediately called arrow function has a body wrapped in parentheses.
  
  > 1 │ const foo = (bar => (bar ? bar.baz : baz))(getBar());
      │                     ^^^^^^^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ The extra parentheses make the function look like a grouped expression, which hides where the function body starts.
  
  ℹ Move the code out of the function, or use a body in braces with a return statement.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.
  
  ℹ Unsafe fix: Use a body in braces with a return statement.
  
    1   │ - const·foo·=·(bar·=>·(bar·?·bar.baz·:·baz))(getBar());
      1 │ + const·foo·=·(bar·=>·{·return·bar·?·bar.baz·:·baz;·})(getBar());
    2 2 │

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const foo = ((bar, baz) => ({ bar, baz }))(bar, baz);

code-block.js:1:28 lint/nursery/noUnreadableIife  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ This immediately called arrow function has a body wrapped in parentheses.
  
  > 1 │ const foo = ((bar, baz) => ({ bar, baz }))(bar, baz);
      │                            ^^^^^^^^^^^^^^
    2 │ 
  
  ℹ The extra parentheses make the function look like a grouped expression, which hides where the function body starts.
  
  ℹ Move the code out of the function, or use a body in braces with a return statement.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.
  
  ℹ Unsafe fix: Use a body in braces with a return statement.
  
    1   │ - const·foo·=·((bar,·baz)·=>·({·bar,·baz·}))(bar,·baz);
      1 │ + const·foo·=·((bar,·baz)·=>·{·return·{·bar,·baz·};·})(bar,·baz);
    2 2 │

Valid

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const bar = getBar();
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const foo = bar ? bar.baz : baz;
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const getBaz = bar => (bar ? bar.baz : baz);
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const qux = getBaz(getBar());
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const quux = (bar => {
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    return bar ? bar.baz : baz;
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})(getBar());