How to use the sdp.writeMediaSection function in sdp

}
      }

      // Calculate intersection of capabilities.
      var commonCapabilities = getCommonCapabilities(
          transceiver.localCapabilities,
          transceiver.remoteCapabilities);

      var hasRtx = commonCapabilities.codecs.filter(function(c) {
        return c.name.toLowerCase() === 'rtx';
      }).length;
      if (!hasRtx && transceiver.sendEncodingParameters[0].rtx) {
        delete transceiver.sendEncodingParameters[0].rtx;
      }

      sdp += SDPUtils.writeMediaSection(transceiver, commonCapabilities,
          'answer', transceiver.stream);
      if (transceiver.rtcpParameters &&
          transceiver.rtcpParameters.reducedSize) {
        sdp += 'a=rtcp-rsize\r\n';
      }
    });

'a=mid:' + transceiver.mid + '\r\n';
          return;
        }
        // Calculate intersection of capabilities.
        var commonCapabilities = self._getCommonCapabilities(
            transceiver.localCapabilities,
            transceiver.remoteCapabilities);

        var hasRtx = commonCapabilities.codecs.filter(function(c) {
          return c.name.toLowerCase() === 'rtx';
        }).length;
        if (!hasRtx && transceiver.sendEncodingParameters[0].rtx) {
          delete transceiver.sendEncodingParameters[0].rtx;
        }

        sdp += SDPUtils.writeMediaSection(transceiver, commonCapabilities,
            'answer', self.localStreams[0]);
        if (transceiver.rtcpParameters &&
            transceiver.rtcpParameters.reducedSize) {
          sdp += 'a=rtcp-rsize\r\n';
        }
      });

this.transceivers.forEach(function(transceiver) {
        if (transceiver.isDatachannel) {
          sdp += 'm=application 0 DTLS/SCTP 5000\r\n' +
              'c=IN IP4 0.0.0.0\r\n' +
              'a=mid:' + transceiver.mid + '\r\n';
          return;
        }
        // Calculate intersection of capabilities.
        var commonCapabilities = self._getCommonCapabilities(
            transceiver.localCapabilities,
            transceiver.remoteCapabilities);

        sdp += SDPUtils.writeMediaSection(transceiver, commonCapabilities,
            'answer', self.localStreams[0]);
      });

}
      }

      // Calculate intersection of capabilities.
      var commonCapabilities = getCommonCapabilities(
          transceiver.localCapabilities,
          transceiver.remoteCapabilities);

      var hasRtx = commonCapabilities.codecs.filter(function(c) {
        return c.name.toLowerCase() === 'rtx';
      }).length;
      if (!hasRtx && transceiver.sendEncodingParameters[0].rtx) {
        delete transceiver.sendEncodingParameters[0].rtx;
      }

      sdp += SDPUtils.writeMediaSection(transceiver, commonCapabilities,
          'answer', transceiver.stream);
      if (transceiver.rtcpParameters &&
          transceiver.rtcpParameters.reducedSize) {
        sdp += 'a=rtcp-rsize\r\n';
      }
    });

tracks.forEach(function(mline, sdpMLineIndex) {
        var transceiver = transceivers[sdpMLineIndex];
        sdp += SDPUtils.writeMediaSection(transceiver,
            transceiver.localCapabilities, 'offer', self.localStreams[0]);
      });

tracks.forEach(function(mline, sdpMLineIndex) {
        var transceiver = transceivers[sdpMLineIndex];
        sdp += SDPUtils.writeMediaSection(transceiver,
            transceiver.localCapabilities, 'offer', self.localStreams[0]);
      });

tracks.forEach(function(mline, sdpMLineIndex) {
        var transceiver = transceivers[sdpMLineIndex];
        sdp += SDPUtils.writeMediaSection(transceiver,
            transceiver.localCapabilities, 'offer', self.localStreams[0]);
      });

tracks.forEach(function(mline, sdpMLineIndex) {
      var transceiver = transceivers[sdpMLineIndex];
      sdp += SDPUtils.writeMediaSection(transceiver,
          transceiver.localCapabilities, 'offer', mline.stream);
      sdp += 'a=rtcp-rsize\r\n';
    });

tracks.forEach(function(mline, sdpMLineIndex) {
        var transceiver = transceivers[sdpMLineIndex];
        sdp += SDPUtils.writeMediaSection(transceiver,
            transceiver.localCapabilities, 'offer', self.localStreams[0]);
      });