noReturnAssign

JavaScript (and super languages)

Summary

Diagnostic Category: lint/nursery/noReturnAssign
This rule doesn’t have a fix.
The default severity of this rule is error.
Sources:
- Same as no-return-assign

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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        "noReturnAssign": "error"
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      }
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    }
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  }
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}

Description

Disallow assignments in return statements.

In return statements, it is common to mistype a comparison operator (such as ==) as an assignment operator (such as =). Moreover, the use of assignments in a return statement is confusing. Return statements are often considered side-effect free.

Examples

Invalid

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function f(a) {
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    return a = 1;
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}

code-block.js:2:12 lint/nursery/noReturnAssign ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Return statements should not contain assignments.
  
    1 │ function f(a) {
  > 2 │     return a = 1;
      │            ^^^^^
    3 │ }
    4 │ 
  
  ℹ Assignments inside return statements are easy to mistake for comparison operators (`==`), and add unexpected side effects to normally-pure code.
    If the assignment is intentional, move it outside of the 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.

Valid

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function f(a) {
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    a = 1;
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    return a;
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}

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function f(a) {
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    return a == 1;
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}