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prefer-classlist-toggle: omit Element#classList.contains() call when fixing #2732

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Merged
merged 8 commits into from
Sep 6, 2025
Merged

prefer-classlist-toggle: omit Element#classList.contains() call when fixing #2732

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b7ae03d
Add tests
fisker Sep 6, 2025
9b92a53
Omit condition
fisker Sep 6, 2025
d6ea570
Update docs
fisker Sep 6, 2025
c0f5be1
Update example
fisker Sep 6, 2025
5164f92
Add tests
fisker Sep 6, 2025
0af12a9
Check ternary
fisker Sep 6, 2025
a4f576d
Update docs
fisker Sep 6, 2025
d922752
Do not insert `, `
fisker Sep 6, 2025
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20 changes: 20 additions & 0 deletions docs/rules/prefer-classlist-toggle.md
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,26 @@ Prefer using [`Element#classList.toggle()`](https://developer.mozilla.org/en-US/

## Examples

```js
// ❌
if (element.classList.contains('className')) {
element.classList.remove('className');
} else {
element.classList.add('className');
}

// ❌
element.classList.contains('className')
? element.classList.remove('className')
: element.classList.add('className');

// ❌
element.classList[element.classList.contains('className') ? 'remove' : 'add']('className')

// ✅
element.classList.toggle('className');
```

```js
// ❌
if (condition) {
Expand Down
64 changes: 48 additions & 16 deletions rules/prefer-classlist-toggle.js
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Original file line number Diff line number Diff line change
Expand Up @@ -78,6 +78,40 @@ const getConditionText = (node, sourceCode, isNegative) => {
return text;
};

const isClassListMethodCall = (node, methods) =>
isMethodCall(node, {
methods,
argumentsLength: 1,
optionalCall: false,
optionalMember: false,
})
&& isClassList(node.callee.object);

const isSameElementAndClassName = (callExpressionA, callExpressionB) =>
isSameReference(callExpressionA.callee.object, callExpressionB.callee.object)
&& isSameReference(callExpressionA.arguments[0], callExpressionB.arguments[0]);

const getClassListContainsCall = (conditionNode, isNegative, addOrRemoveCall) => {
if (!isNegative) {
if (!(conditionNode.type === 'UnaryExpression' && conditionNode.operator === '!' && conditionNode.prefix)) {
return;
}

return getClassListContainsCall(conditionNode.argument, !isNegative, addOrRemoveCall);
}

if (conditionNode.type === 'ChainExpression') {
conditionNode = conditionNode.expression;
}

if (
isClassListMethodCall(conditionNode, ['contains'])
&& isSameElementAndClassName(conditionNode, addOrRemoveCall)
) {
return conditionNode;
}
};

/** @param {import('eslint').Rule.RuleContext} context */
const create = context => {
const {sourceCode} = context;
Expand Down Expand Up @@ -121,37 +155,30 @@ const create = context => {

// `element.classList.add('className');`
// `element.classList.remove('className');`
if (!clauses.every(node =>
isMethodCall(node, {
methods: ['add', 'remove'],
argumentsLength: 1,
optionalCall: false,
optionalMember: false,
})
&& isClassList(node.callee.object),
)) {
if (!clauses.every(node => isClassListMethodCall(node, ['add', 'remove']))) {
return;
}

const [consequent, alternate] = clauses;
if (
(consequent.callee.property.name === alternate.callee.property.name)
|| !isSameReference(consequent.callee.object, alternate.callee.object)
|| !isSameReference(consequent.arguments[0], alternate.arguments[0])
|| !isSameElementAndClassName(consequent, alternate)
) {
return;
}

/** @param {import('eslint').Rule.RuleFixer} fixer */
function * fix(fixer) {
const isOptional = consequent.callee.object.optional || alternate.callee.object.optional;
const elementText = getParenthesizedText(consequent.callee.object.object, sourceCode);
const classNameText = getParenthesizedText(consequent.arguments[0], sourceCode);
const isExpression = node.type === 'ConditionalExpression';
const isNegative = consequent.callee.property.name === 'remove';
const conditionText = getConditionText(node.test, sourceCode, isNegative);
const conditionNode = node.test;
const classListContainsCall = getClassListContainsCall(conditionNode, isNegative, consequent);
const conditionText = classListContainsCall ? '' : getConditionText(conditionNode, sourceCode, isNegative);
const isOptional = consequent.callee.object.optional || alternate.callee.object.optional || classListContainsCall?.callee.object.optional;

let text = `${elementText}${isOptional ? '?' : ''}.classList.toggle(${classNameText}, ${conditionText})`;
let text = `${elementText}${isOptional ? '?' : ''}.classList.toggle(${classNameText}${conditionText ? `, ${conditionText}` : ''})`;

if (!isExpression) {
text = `${text};`;
Expand Down Expand Up @@ -195,9 +222,14 @@ const create = context => {
/** @param {import('eslint').Rule.RuleFixer} fixer */
function * fix(fixer) {
const isNegative = conditionalExpression.consequent.value === 'remove';
const conditionText = getConditionText(conditionalExpression.test, sourceCode, isNegative);
const conditionNode = conditionalExpression.test;
const classListContainsCall = getClassListContainsCall(conditionNode, isNegative, callExpression);
const conditionText = classListContainsCall ? '' : getConditionText(conditionNode, sourceCode, isNegative);

if (conditionText) {
yield fixer.insertTextAfter(callExpression.arguments[0], `, ${conditionText}`);
}

yield fixer.insertTextAfter(callExpression.arguments[0], `, ${conditionText}`);
yield replaceMemberExpressionProperty(fixer, classListMethod, sourceCode, '.toggle');
}

Expand Down
148 changes: 148 additions & 0 deletions test/prefer-classlist-toggle.js
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Original file line number Diff line number Diff line change
Expand Up @@ -212,6 +212,84 @@ test.snapshot({

[].forEach(foo);
`,
// Checking class name existence
outdent`
if (element.classList.contains('className')) {
element.classList.remove('className');
} else {
element.classList.add('className');
}
`,
outdent`
if (element?.classList.contains('className')) {
element.classList.remove('className');
} else {
element.classList.add('className');
}
`,
outdent`
if (element.classList.contains?.('className')) {
element.classList.remove('className');
} else {
element.classList.add('className');
}
`,
outdent`
if (element.classList?.contains('className')) {
element.classList.remove('className');
} else {
element.classList.add('className');
}
`,
outdent`
if (element.classList.notContains('className')) {
element.classList.remove('className');
} else {
element.classList.add('className');
}
`,
outdent`
if (element.classList.contains('not-same-class-name')) {
element.classList.remove('className');
} else {
element.classList.add('className');
}
`,
outdent`
if (element.notClassList.contains('className')) {
element.classList.remove('className');
} else {
element.classList.add('className');
}
`,
outdent`
if (contains('className')) {
element.classList.remove('className');
} else {
element.classList.add('className');
}
`,
outdent`
if (notSameElement.classList.contains('className')) {
element.classList.remove('className');
} else {
element.classList.add('className');
}
`,
outdent`
if (element.classList.contains('className')) {
element.classList.add('className');
} else {
element.classList.remove('className');
}
`,
outdent`
if (!element.classList.contains('className')) {
element.classList.add('className');
} else {
element.classList.remove('className');
}
`,
],
});

Expand Down Expand Up @@ -242,6 +320,62 @@ test.snapshot({

condition ? (( element )).classList.add(className) : element.classList.remove(className);
`,
// Checking class name existence
outdent`
element.classList.contains('className')
? element.classList.remove('className')
: element.classList.add('className')
`,
outdent`
element?.classList.contains('className')
? element.classList.remove('className')
: element.classList.add('className')
`,
outdent`
element.classList.contains?.('className')
? element.classList.remove('className')
: element.classList.add('className')
`,
outdent`
element.classList?.contains('className')
? element.classList.remove('className')
: element.classList.add('className')
`,
outdent`
element.classList.notContains('className')
? element.classList.remove('className')
: element.classList.add('className')
`,
outdent`
element.classList.contains('not-same-class-name')
? element.classList.remove('className')
: element.classList.add('className')
`,
outdent`
element.notClassList.contains('className')
? element.classList.remove('className')
: element.classList.add('className')
`,
outdent`
contains('className')
? element.classList.remove('className')
: element.classList.add('className')
`,
outdent`
notSameElement.classList.contains('className')
? element.classList.remove('className')
: element.classList.add('className')
`,
outdent`
element.classList.contains('className')
? element.classList.add('className')
: element.classList.remove('className')
`,
outdent`
!element.classList.contains('className')
? element.classList.add('className')
: element.classList.remove('className')
`,
],
});

Expand All @@ -268,5 +402,19 @@ test.snapshot({
'element.classList[index % 2 ? "remove" : "add"](className)',
'element.classList[(index % 2) ? "remove" : "add"](className)',
'element.classList[(0, condition) ? "add" : "remove"](className)',
// Checking class name existence
...[
'element.classList.contains("className") ? "remove" : "add"',
'element?.classList.contains("className") ? "remove" : "add"',
'element.classList.contains?.("className") ? "remove" : "add"',
'element.classList?.contains("className") ? "remove" : "add"',
'element.classList.notContains("className") ? "remove" : "add"',
'element.classList.contains("not-same-class-name") ? "remove" : "add"',
'element.notClassList.contains("className") ? "remove" : "add"',
'contains("className") ? "remove" : "add"',
'notSameElement.classList.contains("className") ? "remove" : "add"',
'element.classList.contains("className") ? "add": "remove"',
'!element.classList.contains("className") ? "add": "remove"',
].map(condition => `element.classList[${condition}]("className")`),
],
});
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