How to use the sdp.matchPrefix function in sdp

function(description) {
          var self = this;
          var stream = new MediaStream();
          var receiverList = [];
          var sections = SDPUtils.splitSections(description.sdp);
          var sessionpart = sections.shift();
          var isIceLite = SDPUtils.matchPrefix(sessionpart,
              'a=ice-lite').length > 0;
          this.usingBundle = SDPUtils.matchPrefix(sessionpart,
              'a=group:BUNDLE ').length > 0;
          sections.forEach(function(mediaSection, sdpMLineIndex) {
            var lines = SDPUtils.splitLines(mediaSection);
            var mline = lines[0].substr(2).split(' ');
            var kind = mline[0];
            var rejected = mline[1] === '0';
            var direction = SDPUtils.getDirection(mediaSection, sessionpart);

            var mid = SDPUtils.matchPrefix(mediaSection, 'a=mid:');
            if (mid.length) {
              mid = mid[0].substr(6);
            } else {
              mid = SDPUtils.generateIdentifier();
            }

            // Reject datachannels which are not implemented yet.

// Gets the first SSRC. Note that with RTX there might be multiple
            // SSRCs.
            var remoteSsrc = SDPUtils.matchPrefix(mediaSection, 'a=ssrc:')
                .map(function(line) {
                  return SDPUtils.parseSsrcMedia(line);
                })
                .filter(function(obj) {
                  return obj.attribute === 'cname';
                })[0];
            if (remoteSsrc) {
              cname = remoteSsrc.value;
            }

            var isComplete = SDPUtils.matchPrefix(mediaSection,
                'a=end-of-candidates', sessionpart).length > 0;
            var cands = SDPUtils.matchPrefix(mediaSection, 'a=candidate:')
                .map(function(cand) {
                  return SDPUtils.parseCandidate(cand);
                })
                .filter(function(cand) {
                  return cand.component === '1';
                });
            if (description.type === 'offer' && !rejected) {
              var transports = self.usingBundle && sdpMLineIndex > 0 ? {
                iceGatherer: self.transceivers[0].iceGatherer,
                iceTransport: self.transceivers[0].iceTransport,
                dtlsTransport: self.transceivers[0].dtlsTransport
              } : self._createIceAndDtlsTransports(mid, sdpMLineIndex);

              if (isComplete) {
                transports.iceTransport.setRemoteCandidates(cands);
              }

var remoteCapabilities = SDPUtils.parseRtpParameters(mediaSection);
      var remoteIceParameters;
      var remoteDtlsParameters;
      if (!rejected) {
        remoteIceParameters = SDPUtils.getIceParameters(mediaSection,
            sessionpart);
        remoteDtlsParameters = SDPUtils.getDtlsParameters(mediaSection,
            sessionpart);
        remoteDtlsParameters.role = 'client';
      }
      recvEncodingParameters =
          SDPUtils.parseRtpEncodingParameters(mediaSection);

      var rtcpParameters = SDPUtils.parseRtcpParameters(mediaSection);

      var isComplete = SDPUtils.matchPrefix(mediaSection,
          'a=end-of-candidates', sessionpart).length > 0;
      var cands = SDPUtils.matchPrefix(mediaSection, 'a=candidate:')
          .map(function(cand) {
            return SDPUtils.parseCandidate(cand);
          })
          .filter(function(cand) {
            return cand.component === '1' || cand.component === 1;
          });

      // Check if we can use BUNDLE and dispose transports.
      if ((description.type === 'offer' || description.type === 'answer') &&
          !rejected && usingBundle && sdpMLineIndex > 0 &&
          self.transceivers[sdpMLineIndex]) {
        self._disposeIceAndDtlsTransports(sdpMLineIndex);
        self.transceivers[sdpMLineIndex].iceGatherer =
            self.transceivers[0].iceGatherer;

remoteIceParameters = SDPUtils.getIceParameters(mediaSection,
            sessionpart);
        remoteDtlsParameters = SDPUtils.getDtlsParameters(mediaSection,
            sessionpart);
        remoteDtlsParameters.role = 'client';
      }
      recvEncodingParameters =
          SDPUtils.parseRtpEncodingParameters(mediaSection);

      var rtcpParameters = SDPUtils.parseRtcpParameters(mediaSection);

      // Conference server will send all the ICE candidates in SDP
      //var isComplete = SDPUtils.matchPrefix(mediaSection,
      //    'a=end-of-candidates', sessionpart).length > 0;
      var isComplete = true;
      var cands = SDPUtils.matchPrefix(mediaSection, 'a=candidate:')
          .map(function(cand) {
            return SDPUtils.parseCandidate(cand);
          })
          .filter(function(cand) {
            return cand.component === '1' || cand.component === 1;
          });

      // Check if we can use BUNDLE and dispose transports.
      if ((description.type === 'offer' || description.type === 'answer') &&
          !rejected && usingBundle && sdpMLineIndex > 0 &&
          self.transceivers[sdpMLineIndex]) {
        self._disposeIceAndDtlsTransports(sdpMLineIndex);
        self.transceivers[sdpMLineIndex].iceGatherer =
            self.transceivers[0].iceGatherer;
        self.transceivers[sdpMLineIndex].iceTransport =
            self.transceivers[0].iceTransport;

var cname;
            // Gets the first SSRC. Note that with RTX there might be multiple
            // SSRCs.
            var remoteSsrc = SDPUtils.matchPrefix(mediaSection, 'a=ssrc:')
                .map(function(line) {
                  return SDPUtils.parseSsrcMedia(line);
                })
                .filter(function(obj) {
                  return obj.attribute === 'cname';
                })[0];
            if (remoteSsrc) {
              cname = remoteSsrc.value;
            }

            var isComplete = SDPUtils.matchPrefix(mediaSection,
                'a=end-of-candidates', sessionpart).length > 0;
            var cands = SDPUtils.matchPrefix(mediaSection, 'a=candidate:')
                .map(function(cand) {
                  return SDPUtils.parseCandidate(cand);
                })
                .filter(function(cand) {
                  return cand.component === '1';
                });
            if (description.type === 'offer' && !rejected) {
              var transports = self.usingBundle && sdpMLineIndex > 0 ? {
                iceGatherer: self.transceivers[0].iceGatherer,
                iceTransport: self.transceivers[0].iceTransport,
                dtlsTransport: self.transceivers[0].dtlsTransport
              } : self._createIceAndDtlsTransports(mid, sdpMLineIndex);

              if (isComplete) {

var cname;
            // Gets the first SSRC. Note that with RTX there might be multiple
            // SSRCs.
            var remoteSsrc = SDPUtils.matchPrefix(mediaSection, 'a=ssrc:')
                .map(function(line) {
                  return SDPUtils.parseSsrcMedia(line);
                })
                .filter(function(obj) {
                  return obj.attribute === 'cname';
                })[0];
            if (remoteSsrc) {
              cname = remoteSsrc.value;
            }

            var isComplete = SDPUtils.matchPrefix(mediaSection,
                'a=end-of-candidates', sessionpart).length > 0;
            var cands = SDPUtils.matchPrefix(mediaSection, 'a=candidate:')
                .map(function(cand) {
                  return SDPUtils.parseCandidate(cand);
                })
                .filter(function(cand) {
                  return cand.component === '1';
                });
            if (description.type === 'offer' && !rejected) {
              var transports = self.usingBundle && sdpMLineIndex > 0 ? {
                iceGatherer: self.transceivers[0].iceGatherer,
                iceTransport: self.transceivers[0].iceTransport,
                dtlsTransport: self.transceivers[0].dtlsTransport
              } : self._createIceAndDtlsTransports(mid, sdpMLineIndex);

              if (isComplete) {

function mungeChromeSimulcast(sdp, numberOfSimulcastLayers) {
    let cname;
    let msid;
    const sections = SDPUtils.splitSections(sdp);
    SDPUtils.matchPrefix(sections[1], 'a=ssrc:').forEach(line => {
        const media = SDPUtils.parseSsrcMedia(line);
        if (media.attribute === 'cname') {
            cname = media.value;
        } else if (media.attribute === 'msid') {
            msid = media.value;
        }
    });

    const fidGroup = SDPUtils.matchPrefix(sections[1], 'a=ssrc-group:FID ')[0].substr(17);
    const lines = sections[1].trim().split('\r\n').filter(line => {
        return line.indexOf('a=ssrc:') !== 0 && line.indexOf('a=ssrc-group:') !== 0;
    });
    const simSSRCs = [];
    const [videoSSRC1, rtxSSRC1] = fidGroup.split(' ').map(ssrc => parseInt(ssrc, 10));
    lines.push('a=ssrc:' + videoSSRC1 + ' cname:' + cname);
    lines.push('a=ssrc:' + videoSSRC1 + ' msid:' + msid);

RTCPeerConnection.prototype.setRemoteDescription = function(description) {
    var self = this;
    var streams = {};
    var receiverList = [];
    var sections = SDPUtils.splitSections(description.sdp);
    var sessionpart = sections.shift();
    var isIceLite = SDPUtils.matchPrefix(sessionpart,
        'a=ice-lite').length > 0;
    var usingBundle = SDPUtils.matchPrefix(sessionpart,
        'a=group:BUNDLE ').length > 0;
    var iceOptions = SDPUtils.matchPrefix(sessionpart,
        'a=ice-options:')[0];
    if (iceOptions) {
      this.canTrickleIceCandidates = iceOptions.substr(14).split(' ')
          .indexOf('trickle') >= 0;
    } else {
      this.canTrickleIceCandidates = false;
    }

    sections.forEach(function(mediaSection, sdpMLineIndex) {
      var lines = SDPUtils.splitLines(mediaSection);
      var mline = lines[0].substr(2).split(' ');
      var kind = mline[0];
      var rejected = mline[1] === '0';
      var direction = SDPUtils.getDirection(mediaSection, sessionpart);
      var remoteMsid = SDPUtils.parseMsid(mediaSection);