How to use the tinode-sdk.DEL_CHAR function in tinode-sdk

handleTopicUpdateRequest(topicName, pub, priv, permissions) {
    const topic = this.tinode.getTopic(topicName);
    if (topic) {
      const params = {};
      if (pub) {
        params.public = pub;
      }
      if (priv) {
        params.private = (priv === Tinode.DEL_CHAR) ?
          Tinode.DEL_CHAR : {comment: priv};
      }
      if (permissions) {
        params.defacs = permissions;
      }
      topic.setMeta({desc: params}).catch((err) => {
        this.handleError(err.message, 'err');
      });
    }
  }

handleClear(e) {
    e.preventDefault();
    if (this.state.edited) {
      this.props.onSearchContacts(Tinode.DEL_CHAR);
    }
    this.setState({search: '', edited: false});
  }

handlePrivateUpdate(comment) {
    comment = comment.trim().substring(0, MAX_TITLE_LENGTH);
    if (this.state.private !== comment) {
      this.setState({private: comment});
      this.props.onTopicDescUpdate(this.props.topic, null, comment || Tinode.DEL_CHAR);
    }
  }

handleImageChanged(img) {
    this.setState({avatar: img});
    this.props.onUpdateAccount(undefined, vcard(null, img || Tinode.DEL_CHAR));
  }

handleTopicUpdateRequest(topicName, pub, priv, permissions) {
    const topic = this.tinode.getTopic(topicName);
    if (topic) {
      const params = {};
      if (pub) {
        params.public = pub;
      }
      if (priv) {
        params.private = (priv === Tinode.DEL_CHAR) ?
          Tinode.DEL_CHAR : {comment: priv};
      }
      if (permissions) {
        params.defacs = permissions;
      }
      topic.setMeta({desc: params}).catch((err) => {
        this.handleError(err.message, 'err');
      });
    }
  }