parser: ArrayLiteral as computed property key rejected in class bodies
class C { [[]]() {} } is rejected with "Unexpected token", but the grammar is valid per ECMA-262 and every other major parser accepts it.
Reproduction
Playground link
Steps:
mkdir /tmp/oxc-repro && cd /tmp/oxc-repro
npm init -y
npm install oxc-parser
node -e "
const { parseSync } = require('oxc-parser');
// ✗ Rejected in class body
const r1 = parseSync('input.js', 'class C { [[]]() {} }');
console.log('class [[]]():', r1.errors.length ? 'ERROR: ' + r1.errors[0].message : 'OK');
// ✗ Also rejected with non-empty inner array
const r2 = parseSync('input.js', 'class C { [[1]]() {} }');
console.log('class [[1]]():', r2.errors.length ? 'ERROR: ' + r2.errors[0].message : 'OK');
// ✗ Also rejected as field
const r3 = parseSync('input.js', 'class C { [[]] = 1 }');
console.log('class [[]] = 1:', r3.errors.length ? 'ERROR: ' + r3.errors[0].message : 'OK');
// ✓ Accepted in object literal
const r4 = parseSync('input.js', 'const o = { [[]]() {} }');
console.log('obj [[]]():', r4.errors.length ? 'ERROR: ' + r4.errors[0].message : 'OK');
"Expected output:
class [[]](): OK
class [[1]](): OK
class [[]] = 1: OK
obj [[]](): OK
Actual output (oxc-parser 0.129.0):
class [[]](): ERROR: Unexpected token
class [[1]](): ERROR: Unexpected token
class [[]] = 1: ERROR: Unexpected token
obj [[]](): OK
V8 cross-check (confirming it's valid JS):
echo 'class C { [[]]() {} }' > /tmp/test.js
node --check /tmp/test.js && echo "V8: OK" || echo "V8: ERROR"
# → V8: OKSpec reference
ECMA-262 §13.2.5.2 ComputedPropertyName: [ AssignmentExpression ]
AssignmentExpression → … → PrimaryExpression → ArrayLiteral → [ ElementList_opt ]
An empty ArrayLiteral ([]) is a valid AssignmentExpression, so [[]] as a class element's computed key is grammatically correct. The same grammar applies to both object literals and class bodies — there is no restriction that excludes ArrayLiteral from class ComputedPropertyName.
Parser matrix
| Parser |
Version |
class { [[]]() {} } |
{ [[]]() {} } (obj) |
| V8 (node --check) |
v25.9.0 |
✅ accepts |
✅ accepts |
| Acorn |
latest |
✅ accepts |
✅ accepts |
| Babel |
7.29.3 |
✅ accepts |
✅ accepts |
| TypeScript |
6.0.3 |
✅ accepts |
✅ accepts |
| SWC |
1.15.33 |
✅ accepts |
✅ accepts |
| esbuild |
0.28.0 |
✅ accepts |
✅ accepts |
| OXC |
0.129.0 |
❌ rejects |
✅ accepts |
OXC is the only parser that rejects this syntax, and only in class bodies.
parser:
ArrayLiteralas computed property key rejected in class bodiesclass C { [[]]() {} }is rejected with "Unexpected token", but the grammar is valid per ECMA-262 and every other major parser accepts it.Reproduction
Playground link
Steps:
Expected output:
Actual output (oxc-parser 0.129.0):
V8 cross-check (confirming it's valid JS):
Spec reference
ECMA-262 §13.2.5.2 ComputedPropertyName:
[AssignmentExpression]AssignmentExpression → … → PrimaryExpression → ArrayLiteral →
[ElementList_opt]An empty
ArrayLiteral([]) is a valid AssignmentExpression, so[[]]as a class element's computed key is grammatically correct. The same grammar applies to both object literals and class bodies — there is no restriction that excludesArrayLiteralfrom classComputedPropertyName.Parser matrix
class { [[]]() {} }{ [[]]() {} }(obj)OXC is the only parser that rejects this syntax, and only in class bodies.