How to use the sdp.writeSessionBoilerplate function in sdp

RTCPeerConnection.prototype.createAnswer = function() {
    var sdp = SDPUtils.writeSessionBoilerplate(this._sdpSessionId);
    if (this.usingBundle) {
      sdp += 'a=group:BUNDLE ' + this.transceivers.map(function(t) {
        return t.mid;
      }).join(' ') + '\r\n';
    }
    this.transceivers.forEach(function(transceiver, sdpMLineIndex) {
      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;
      }

      // FIXME: look at direction.
      if (transceiver.stream) {
        var localTrack;

// Create M-lines for recvonly streams.
    while (numAudioTracks > 0 || numVideoTracks > 0) {
      if (numAudioTracks > 0) {
        this._createTransceiver('audio');
        numAudioTracks--;
      }
      if (numVideoTracks > 0) {
        this._createTransceiver('video');
        numVideoTracks--;
      }
    }
    // reorder tracks
    var transceivers = sortTracks(this.transceivers);

    var sdp = SDPUtils.writeSessionBoilerplate();
    transceivers.forEach(function(transceiver, sdpMLineIndex) {
      // For each track, create an ice gatherer, ice transport,
      // dtls transport, potentially rtpsender and rtpreceiver.
      var track = transceiver.track;
      var kind = transceiver.kind;
      var mid = SDPUtils.generateIdentifier();
      transceiver.mid = mid;

      if (!transceiver.iceGatherer) {
        transceiver.iceGatherer = self.usingBundle && sdpMLineIndex > 0 ?
            transceivers[0].iceGatherer :
            self._createIceGatherer(mid, sdpMLineIndex);
      }

      var localCapabilities = window.RTCRtpSender.getCapabilities(kind);
      // filter RTX until additional stuff needed for RTX is implemented

RTCPeerConnection.prototype.createAnswer = function() {
    var sdp = SDPUtils.writeSessionBoilerplate(this._sdpSessionId);
    if (this.usingBundle) {
      sdp += 'a=group:BUNDLE ' + this.transceivers.map(function(t) {
        return t.mid;
      }).join(' ') + '\r\n';
    }
    this.transceivers.forEach(function(transceiver, sdpMLineIndex) {
      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;
      }

      // FIXME: look at direction.
      if (transceiver.stream) {
        var localTrack;

wantReceive: true
        });
        numAudioTracks--;
      }
      if (numVideoTracks > 0) {
        tracks.push({
          kind: 'video',
          wantReceive: true
        });
        numVideoTracks--;
      }
    }
    // reorder tracks
    tracks = sortTracks(tracks);

    var sdp = SDPUtils.writeSessionBoilerplate();
    var transceivers = [];
    tracks.forEach(function(mline, sdpMLineIndex) {
      // For each track, create an ice gatherer, ice transport,
      // dtls transport, potentially rtpsender and rtpreceiver.
      var track = mline.track;
      var kind = mline.kind;
      var mid = SDPUtils.generateIdentifier();

      var transports = self.usingBundle && sdpMLineIndex > 0 ? {
        iceGatherer: transceivers[0].iceGatherer,
        iceTransport: transceivers[0].iceTransport,
        dtlsTransport: transceivers[0].dtlsTransport
      } : self._createIceAndDtlsTransports(mid, sdpMLineIndex);

      var localCapabilities = RTCRtpSender.getCapabilities(kind);
      // filter RTX until additional stuff needed for RTX is implemented

window.RTCPeerConnection.prototype.createAnswer = function() {
      var self = this;

      var sdp = SDPUtils.writeSessionBoilerplate();
      this.transceivers.forEach(function(transceiver) {
        // Calculate intersection of capabilities.
        var commonCapabilities = self._getCommonCapabilities(
            transceiver.localCapabilities,
            transceiver.remoteCapabilities);

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

      var desc = new RTCSessionDescription({
        type: 'answer',
        sdp: sdp
      });
      if (arguments.length && typeof arguments[0] === 'function') {
        window.setTimeout(arguments[0], 0, desc);

window.RTCPeerConnection.prototype.createAnswer = function() {
      var self = this;

      var sdp = SDPUtils.writeSessionBoilerplate();
      if (this.usingBundle) {
        sdp += 'a=group:BUNDLE ' + this.transceivers.map(function(t) {
          return t.mid;
        }).join(' ') + '\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);

window.RTCPeerConnection.prototype.createAnswer = function() {
      var self = this;

      var sdp = SDPUtils.writeSessionBoilerplate();
      if (this.usingBundle) {
        sdp += 'a=group:BUNDLE ' + this.transceivers.map(function(t) {
          return t.mid;
        }).join(' ') + '\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);

window.RTCPeerConnection.prototype.createAnswer = function() {
      var self = this;

      var sdp = SDPUtils.writeSessionBoilerplate();
      if (this.usingBundle) {
        sdp += 'a=group:BUNDLE ' + this.transceivers.map(function(t) {
          return t.mid;
        }).join(' ') + '\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);

window.RTCPeerConnection.prototype.createAnswer = function() {
      var self = this;

      var sdp = SDPUtils.writeSessionBoilerplate();
      if (this.usingBundle) {
        sdp += 'a=group:BUNDLE ' + this.transceivers.map(function(t) {
          return t.mid;
        }).join(' ') + '\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);