"Operator precedence": yield and =; ?? and ||

[js-choi]

MDN URL: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Operator_Precedence

@bakkot brought this to my attention: There are at least two inaccuracies in the JavaScript operator-precedence table.

• yield/yield * have equal precedence with = and the other assignment operators (AssignmentExpression). This is why x = yield 1 is valid in a generator, while x + yield 1 is invalid.
• || and ?? have equal precedence (ShortCircuitExpression). Their grammar is such that they are mutually exclusive—they cannot be used together without parentheses—but they nevertheless have equal precedence.

As an aside, I also find puzzling the inclusion of = as an operator but the exclusion of =>. Both tokens create expressions. And neither = nor => are actually binary operators over two expressions (both their left sides are evaluated as variable bindings, not expressions). = and => even have equal precedence in the spec (AssignmentExpression again). Calling = but not => an operator seems arbitrary.

MDN Content page report details

• Folder: en-us/web/javascript/reference/operators/operator_precedence
• MDN URL: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Operator_Precedence
• GitHub URL: https://github.com/mdn/content/blob/main/files/en-us/web/javascript/reference/operators/operator_precedence/index.html
• Last commit: 820366a
• Document last modified: 2021-04-19T08:04:23.000Z