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Asked: 2026-05-29T16:06:08+00:00

I’m building a JavaScript parser and there seem to be some differing opinions. ECMA-262

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I’m building a JavaScript parser and there seem to be some differing opinions.

ECMA-262 seems to suggest that it is not optional, but Wikipedia says it is.

ECMA-262:

SwitchStatement : switch ( Expression ) CaseBlock

CaseBlock : { CaseClausesopt }

{ CaseClausesopt DefaultClause CaseClausesopt }

Wikipedia:

case default: is optional.

Does Wikipedia just mean that you can literally write case default: if you want?

EDIT

Just realised I was reading ECMA wrong. The first case block option i.e. { CaseClausesopt } allows you to miss out the default block. Case closed (if you’ll pardon the pun).

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1 Answer

  1. Editorial Team

    A CaseBlock can be either of the following:

    • { CaseClausesopt }
    • { CaseClausesopt DefaultClause CaseClausesopt }

    That’s sort of a clumsy way of saying that there can be at most one DefaultClause, and you can put it anywhere in the CaseBlock.

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