noUnsafePlusOperands

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JavaScript (and super languages)

Summary

Rule available since: v2.4.10
Diagnostic Category: lint/nursery/noUnsafePlusOperands
This rule doesn’t have a fix.
The default severity of this rule is information.
This rule belongs to the following domains:
- types
Sources:
- Same as @typescript-eslint/restrict-plus-operands

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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        "noUnsafePlusOperands": "error"
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      }
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    }
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  }
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}

Description

Disallow + operations with operands that are known to be unsafe.

This rule uses type information to report + and += operations that are very likely mistakes at runtime, such as mixing number with bigint or using object-like, symbol, unknown, or never values as operands.

This port intentionally does not support the original rule’s options. It keeps the upstream default behavior for no-option usage and always checks compound += assignments.

Examples

Invalid

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const value = 1n + 1;

/invalid-bigint-plus-number.ts:1:15 lint/nursery/noUnsafePlusOperands ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Numeric + operations must use either two bigint values or two number values.
  
  > 1 │ const value = 1n + 1;
      │               ^^^^^^
    2 │ 
  
  ℹ This operation mixes number with bigint.
  
  > 1 │ const value = 1n + 1;
      │               ^^^^^^
    2 │ 
  
  ℹ Convert one side so both operands use the same numeric type before applying + or +=.
  
  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 value = 1 + 1n;

/invalid-number-plus-bigint.ts:1:15 lint/nursery/noUnsafePlusOperands ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Numeric + operations must use either two bigint values or two number values.
  
  > 1 │ const value = 1 + 1n;
      │               ^^^^^^
    2 │ 
  
  ℹ This operation mixes number with bigint.
  
  > 1 │ const value = 1 + 1n;
      │               ^^^^^^
    2 │ 
  
  ℹ Convert one side so both operands use the same numeric type before applying + or +=.
  
  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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declare let count: number;
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count += 1n;

/invalid-bigint-add-assign.ts:2:1 lint/nursery/noUnsafePlusOperands ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Numeric + operations must use either two bigint values or two number values.
  
    1 │ declare let count: number;
  > 2 │ count += 1n;
      │ ^^^^^^^^^^^
    3 │ 
  
  ℹ This operation mixes number with bigint.
  
    1 │ declare let count: number;
  > 2 │ count += 1n;
      │ ^^^^^^^^^^^
    3 │ 
  
  ℹ Convert one side so both operands use the same numeric type before applying + or +=.
  
  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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const sum = 1 + 2;

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const message = "value: " + 1;

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let total = 1n;
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total += 2n;