Interface properties are declared using interface-property-declarations:

interface-property-declaration

attributes_optnew _opt type identifier { interface-accessors }

interface-accessors

attributes_opt get ;

attributes_opt set ;

attributes_opt get ; attributes_opt set ;

attributes_opt set ; attributes_opt get ;

The attributes, type, and identifier of an interface property declaration have the same meaning as those of a property declaration in a class (17.6).

The accessors of an interface property declaration correspond to the accessors of a class property declaration (17.6.2), except that the accessor body must always be a semicolon. Thus, the accessors simply indicate whether the property is read-write, read-only, or write-only.