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no-array-reduce - enable reporting of optional chaining and calling of .reduce() #2721

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Merged
sindresorhus merged 6 commits into from
Sep 1, 2025
Merged

no-array-reduce - enable reporting of optional chaining and calling of .reduce() #2721

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c0eb380
`no-array-reduce` - add test cases for optional reduce
ipanasenko Aug 29, 2025
f251dc0
check also for optional
ipanasenko Sep 1, 2025
99b8ac7
also optional call
ipanasenko Sep 1, 2025
4439bc4
Merge branch 'main' into reduce-optional
ipanasenko Sep 1, 2025
1d444f2
revert for `.call()` and `.apply()`
ipanasenko Sep 1, 2025
8240f4f
Add `optionalCall: false` back
fisker Sep 1, 2025
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6 changes: 0 additions & 6 deletions rules/no-array-reduce.js
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Original file line number Diff line number Diff line change
Expand Up @@ -16,8 +16,6 @@ const cases = [
methods: ['reduce', 'reduceRight'],
minimumArguments: 1,
maximumArguments: 2,
optionalCall: false,
optionalMember: false,
})
&& !isNodeValueNotFunction(callExpression.arguments[0]),
getMethodNode: callExpression => callExpression.callee.property,
Expand Down Expand Up @@ -47,8 +45,6 @@ const cases = [
test: callExpression =>
isMethodCall(callExpression, {
method: 'call',
optionalCall: false,
optionalMember: false,
})
&& isArrayPrototypeProperty(callExpression.callee.object, {
properties: ['reduce', 'reduceRight'],
Expand All @@ -64,8 +60,6 @@ const cases = [
test: callExpression =>
isMethodCall(callExpression, {
method: 'apply',
optionalCall: false,
optionalMember: false,
})
&& isArrayPrototypeProperty(callExpression.callee.object, {
properties: ['reduce', 'reduceRight'],
Expand Down
4 changes: 4 additions & 0 deletions test/no-array-reduce.js
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Expand Up @@ -12,6 +12,8 @@ test({
'a[b.reduce]()',
'a(b.reduce)',
'a.reduce()',
'a?.reduce()',
'a.reduce?.()',
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@fisker fisker Sep 1, 2025

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It doesn't make sense to allow optional call.

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@ipanasenko ipanasenko Sep 1, 2025

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Added it because I saw it in no-array-sort and no-array-reverse 🤷‍♂️
https://github.com/sindresorhus/eslint-plugin-unicorn/blob/main/test/no-array-sort.js#L14
https://github.com/sindresorhus/eslint-plugin-unicorn/blob/main/test/no-array-reverse.js#L14

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@fisker fisker Sep 1, 2025

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They are valid cases in these two rules, and they both use optionalCall: false,

eslint-plugin-unicorn/rules/shared/no-array-mutate-rule.js

Line 17 in d96dfb7

optionalCall: false,

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@fisker fisker Sep 1, 2025

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I mean a?.reduce() should be invalid, but a.reduce?.() should be valid.

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@fisker fisker Sep 1, 2025

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Sorry, I comment this in a misleading place, I mean L112

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@ipanasenko ipanasenko Sep 1, 2025 •
edited
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I don't understand, sorry :(
Why one should be valid and another invalid? I thought this rule finds usages of reduce, and reports it (except trivial callback cases, if corresponding option is provided). Why reporting of a?.reduce() should be different to a.reduce?.() and a.reduce()?
Or array.reduce((str, item) => str += item, "") different to array?.reduce((str, item) => str += item, "") and array.reduce?.((str, item) => str += item, "") if we talk about L112?

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Because it's doesn't make sense to check Array#reduce, if user using foo.reduce?.() then foo can be a non-array object.

Explained in this commit 8240f4f (#2721)

'a.reduce(1, 2, 3)',
'a.reduce(b, c, d)',
'[][reduce].call()',
Expand Down Expand Up @@ -106,6 +108,8 @@ test({
].flatMap(testCase => [testCase, testCase.replace('reduce', 'reduceRight')]),
invalid: [
'array.reduce((str, item) => str += item, "")',
'array?.reduce((str, item) => str += item, "")',
'array.reduce?.((str, item) => str += item, "")',
outdent`
array.reduce((obj, item) => {
obj[item] = null;
Expand Down
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