noFunctionAssign

JavaScript (and super languages)

Summary

• Rule available since: v1.0.0
• Diagnostic Category: lint/suspicious/noFunctionAssign
• This rule is recommended, which means is enabled by default.
• This rule doesn’t have a fix.
• The default severity of this rule is error.
• Sources:
  • Same as no-func-assign

How to configure

biome.json

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

Description

Disallow reassigning function declarations.

Examples

Invalid

function foo() { };
foo = bar;

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

  ✖ Do not reassign a function declaration.
  
  > 1 │ function foo() { };
      │          ^^^
    2 │ foo = bar;
    3 │ 
  
  ℹ Reassigned here.
  
    1 │ function foo() { };
  > 2 │ foo = bar;
      │ ^^^
    3 │ 
  
  ℹ Use a local variable instead.
  

function foo() {
    foo = bar;
 }

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

  ✖ Do not reassign a function declaration.
  
  > 1 │ function foo() {
      │          ^^^
    2 │     foo = bar;
    3 │  }
  
  ℹ Reassigned here.
  
    1 │ function foo() {
  > 2 │     foo = bar;
      │     ^^^
    3 │  }
    4 │ 
  
  ℹ Use a local variable instead.
  

foo = bar;
function foo() { };

code-block.js:2:10 lint/suspicious/noFunctionAssign ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Do not reassign a function declaration.
  
    1 │ foo = bar;
  > 2 │ function foo() { };
      │          ^^^
    3 │ 
  
  ℹ Reassigned here.
  
  > 1 │ foo = bar;
      │ ^^^
    2 │ function foo() { };
    3 │ 
  
  ℹ Reassignment happens here because the function declaration is hoisted.
  
  ℹ Use a local variable instead.
  

[foo] = bar;
function foo() { };

code-block.js:2:10 lint/suspicious/noFunctionAssign ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Do not reassign a function declaration.
  
    1 │ [foo] = bar;
  > 2 │ function foo() { };
      │          ^^^
    3 │ 
  
  ℹ Reassigned here.
  
  > 1 │ [foo] = bar;
      │  ^^^
    2 │ function foo() { };
    3 │ 
  
  ℹ Reassignment happens here because the function declaration is hoisted.
  
  ℹ Use a local variable instead.
  

({ x: foo = 0 } = bar);
function foo() { };

code-block.js:2:10 lint/suspicious/noFunctionAssign ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Do not reassign a function declaration.
  
    1 │ ({ x: foo = 0 } = bar);
  > 2 │ function foo() { };
      │          ^^^
    3 │ 
  
  ℹ Reassigned here.
  
  > 1 │ ({ x: foo = 0 } = bar);
      │       ^^^
    2 │ function foo() { };
    3 │ 
  
  ℹ Reassignment happens here because the function declaration is hoisted.
  
  ℹ Use a local variable instead.
  

function foo() {
    [foo] = bar;
 }

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

  ✖ Do not reassign a function declaration.
  
  > 1 │ function foo() {
      │          ^^^
    2 │     [foo] = bar;
    3 │  }
  
  ℹ Reassigned here.
  
    1 │ function foo() {
  > 2 │     [foo] = bar;
      │      ^^^
    3 │  }
    4 │ 
  
  ℹ Use a local variable instead.
  

(function () {
    ({ x: foo = 0 } = bar);
    function foo() { };
 })();

code-block.js:3:14 lint/suspicious/noFunctionAssign ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Do not reassign a function declaration.
  
    1 │ (function () {
    2 │     ({ x: foo = 0 } = bar);
  > 3 │     function foo() { };
      │              ^^^
    4 │  })();
    5 │ 
  
  ℹ Reassigned here.
  
    1 │ (function () {
  > 2 │     ({ x: foo = 0 } = bar);
      │           ^^^
    3 │     function foo() { };
    4 │  })();
  
  ℹ Reassignment happens here because the function declaration is hoisted.
  
  ℹ Use a local variable instead.
  

Valid

function foo() {
    var foo = bar;
 }

function foo(foo) {
    foo = bar;
 }

function foo() {
    var foo;
    foo = bar;
 }

var foo = () => {};
foo = bar;

var foo = function() {};
foo = bar;

var foo = function() {
    foo = bar;
 };

import bar from 'bar';
function foo() {
    var foo = bar;
}

Related links

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