useNamedFunction (JavaScript)

Language JavaScript (and super languages)

Summary

Rule available since: v2.6.0
Diagnostic Category: lint/nursery/useNamedFunction
This rule doesn’t have a fix.
The default severity of this rule is information.
Sources:
- Inspired from func-names

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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        "useNamedFunction": "error"
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      }
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    }
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  }
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}

Description

Require function expressions to have a name.

A function expression is a function written with the function keyword inside other code, for example when it is passed to another function or stored in a property. Unlike a function declaration, it does not need a name.

When a function has no name, error messages and debugging tools can show it as <anonymous>, which makes it harder to find where an error came from.

JavaScript automatically names some functions, such as a function stored in a variable. This rule still asks for a name in those cases, so that every function is named the same way no matter where it is written.

The rule also checks async functions, generator functions (function*), and export default function() {}. Arrow functions and methods are not checked.

Examples

Invalid

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Foo.prototype.bar = function() {};

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

  ℹ This function has no name.
  
  > 1 │ Foo.prototype.bar = function() {};
      │                     ^^^^^^^^
    2 │ 
  
  ℹ Error messages and debugging tools can show a function without a name as <anonymous>, which makes it harder to find where an error came from.
  
  ℹ Give this function a name.
  
  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.

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const cat = {
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    meow: function() {}
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};

code-block.js:2:11 lint/nursery/useNamedFunction ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ This function has no name.
  
    1 │ const cat = {
  > 2 │     meow: function() {}
      │           ^^^^^^^^
    3 │ };
    4 │ 
  
  ℹ Error messages and debugging tools can show a function without a name as <anonymous>, which makes it harder to find where an error came from.
  
  ℹ Give this function a name.
  
  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.

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(function() {
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    // ...
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}());

code-block.js:1:2 lint/nursery/useNamedFunction ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ This function has no name.
  
  > 1 │ (function() {
      │  ^^^^^^^^
    2 │     // ...
    3 │ }());
  
  ℹ Error messages and debugging tools can show a function without a name as <anonymous>, which makes it harder to find where an error came from.
  
  ℹ Give this function a name.
  
  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.

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export default function() {}

code-block.js:1:16 lint/nursery/useNamedFunction ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ This function has no name.
  
  > 1 │ export default function() {}
      │                ^^^^^^^^
    2 │ 
  
  ℹ Error messages and debugging tools can show a function without a name as <anonymous>, which makes it harder to find where an error came from.
  
  ℹ Give this function a name.
  
  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.

Valid

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Foo.prototype.bar = function bar() {};
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const cat = {
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    meow() {}
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};
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(function setup() {
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    // ...
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}());
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const handler = () => {};
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export default function main() {}