useIterableCallbackReturn

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JavaScript (and super languages)

Summary

Rule available since: v2.0.0
Diagnostic Category: lint/nursery/useIterableCallbackReturn
This rule doesn’t have a fix.
The default severity of this rule is error.
Sources:
- Same as array-callback-return

Description

Enforce consistent return values in iterable callbacks.

This rule ensures that callbacks passed to certain iterable methods either always return a value or never return a value, depending on the method’s requirements.

Note that async and generator callbacks are ignored as they always return Promise or Generator respectively.

Methods and Their Requirements

The following methods require a return in their callback:

every
filter
find
findIndex
findLast
findLastIndex
flatMap
map
reduce
reduceRight
some
sort
toSorted — from (when called on Array)

A return value is disallowed in the method forEach.

Examples

Invalid

1
[].map(() => {
2
    // Missing return value
3
});

code-block.js:1:4 lint/nursery/useIterableCallbackReturn ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This callback passed to map() iterable method should always return a value.
  
  > 1 │ [].map(() => {
      │    ^^^
    2 │     // Missing return value
    3 │ });
  
  ℹ Add a return with a value to this callback.

1
[].forEach(() => {
2
    return 1; // Should not return a value
3
});

code-block.js:1:4 lint/nursery/useIterableCallbackReturn ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This callback passed to forEach() iterable method should not return a value.
  
  > 1 │ [].forEach(() => {
      │    ^^^^^^^
    2 │     return 1; // Should not return a value
    3 │ });
  
  ℹ Either remove this return or remove the returned value.
  
  > 1 │ [].forEach(() => {
      │                   
  > 2 │     return 1; // Should not return a value
      │     ^^^^^^^
    3 │ });
    4 │

Valid

1
[].map(() => {
2
    return 1; // Correctly returns a value
3
});

1
[].forEach(() => {
2
    // No return value, which is correct
3
});

How to configure

1
{
2
  "linter": {
3
    "rules": {
4
      "nursery": {
5
        "useIterableCallbackReturn": "error"
6
      }
7
    }
8
  }
9
}