propertyName = prop => {
	if (SAFE_IDENTIFIER.test(prop) && !RESERVED_IDENTIFIER.has(prop)) {
		return prop;
	}
	return JSON.stringify(prop);
}
@summary Returns a valid JS property name for the given property.
Certain strings like "default", "null", and names with whitespace are not
valid JS property names, so they are returned as strings.
@param {string} prop property name to analyze
@returns {string} valid JS property name