write(message, options) {
        const json = {}, source = message;
        for (const field of this.fields) {
            // field is not part of a oneof, simply write as is
            if (!field.oneof) {
                let jsonValue = this.field(field, source[field.localName], options);
                if (jsonValue !== undefined)
                    json[options.useProtoFieldName ? field.name : field.jsonName] = jsonValue;
                continue;
            }
            // field is part of a oneof
            const group = source[field.oneof];
            if (group.oneofKind !== field.localName)
                continue; // not selected, skip
            const opt = field.kind == 'scalar' || field.kind == 'enum'
                ? Object.assign(Object.assign({}, options), { emitDefaultValues: true }) : options;
            let jsonValue = this.field(field, group[field.localName], opt);
            assert_1.assert(jsonValue !== undefined);
            json[options.useProtoFieldName ? field.name : field.jsonName] = jsonValue;
        }
        return json;
    }
Converts the message to a JSON object, based on the field descriptors.