自作ノード開発において，jsファイルからhtmlファイル内のscriptタグの関数を叩きたい

Question

#やりたいこと
node-red-contrib-browser-utilsのcameraノードの改変を考えています．このノードは，元々ボタンを押したときにPCのカメラから写真を撮影するノードなのですが，これを改変してこのノードになんらかのinputが入ってきた場合に写真を撮影するノードに書き換えたいと思っています．

<!--
  Copyright 2013, 2016, 2019 IBM Corp.
  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at
  http://www.apache.org/licenses/LICENSE-2.0
  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
-->

<script type="text/x-red" data-template-name="camera">
    <div class="form-row">
        <label for="node-input-name"><i class="fa fa-tag"></i> Name</label>
        <input type="text" id="node-input-name" placeholder="Camera">
    </div>
</script>

<script type="text/x-red" data-help-name="camera">
    <p>A simple camera node to capture the current image from the device webcam</p>
    <p>Usage:</p>
    <ol>
        <li>Add the camera node to your flow</li>
        <li>Click the <code>button</code> capture an image from the webcam</li>
    </ol>
    <p>The <code>png</code> image is sent as the <code>msg.payload</code> object</p>
    <p>Supported browsers</p>
    <ul>
      <li>Chrome</li>
      <li>Firefox</li>
    </ul>
</script>


<script type="text/javascript">
    (function() {
        navigator.getUserMedia = navigator.getUserMedia || navigator.webkitGetUserMedia || navigator.mozGetUserMedia || navigator.msGetUserMedia;
        window.URL = window.URL || window.webkitURL || window.mozURL || window.msURL;

        window.video = document.createElement('video')
        window.canvas = document.createElement('canvas')
        canvas.style.display = 'none'
        canvas.style.display = 'none'
        var id

        function onCanPlay(evt) {
          video.removeEventListener('canplay', onCanPlay, false)
          var width   = 320
          var height  = video.videoHeight / (video.videoWidth / width)

          if (isNaN(height)) {
            height = width / (4 / 3)
          }

          setTimeout(function(evt) {

            video.setAttribute('width', width)
            video.setAttribute('height', height)
            canvas.setAttribute('width', width)
            canvas.setAttribute('height', height)

            var ctx = canvas.getContext('2d')
            ctx.drawImage(video, 0, 0, width, height)

            canvas.toBlob(function(blob) {
              uploadRecord(id, blob)
            })
          }, 2000)
        }

        function onStreamReady(id, stream) {
          // As of Chrome 71 createObjectURL is dropped so try direct
          // access first
          // https://developer.mozilla.org/en-US/docs/Web/API/HTMLMediaElement/srcObject
          try {
            video.srcObject = stream;
          } catch (error) {
            video.src = window.URL.createObjectURL(stream)
          }

          video.addEventListener('canplay', onCanPlay, false)

          video.play()
        }

        function onVideoPlaying(id, evt) {
          canvas.style.height = video.clientHeight + 'px'
          canvas.style.width = video.clientWidth + 'px'

          var ctx = canvas.getContext('2d')
          ctx.drawImage(video, 0, 0)

          canvas.toBlob(function(blob) {
            uploadRecord(id, blob)
          })
        }

        function setCameraStatus(record, id) {
          $.getJSON('node-red-camera/status', {status: record, id: id})
            .done(function () {})
            .fail(function (err) {
              console.log(err);
            })
            .always(function () {});
        }

        function takeSnapshot(id) {
          const constraints = {video : true, audio : false};
          navigator.mediaDevices.getUserMedia(constraints)
            .then(function(stream) {
              setCameraStatus(true, id)
              onStreamReady(id, stream)
            })
            .catch(function(err) {
                window.alert('Your browser does not support the camera node')
                console.log(err)
            })
        }

        function uploadRecord(id, blob) {
            var xhr = new XMLHttpRequest()
            xhr.open('POST', 'node-red-camera/' + id, true)
            xhr.send(blob)
        }

        RED.nodes.registerType('camera', {
            category: 'input',
            defaults: {
                name: {value: ''}
            },
            color: 'rgb(215, 201, 194)',
            inputs: 0,
            outputs: 1,
            icon: 'camera.png',
            paletteLabel: 'camera',
            label: function() {
                return this.name || 'camera';
            },
            labelStyle: function() {
                return this.name ? 'node_label_italic' : '';
            },
            button: {
                onclick: function(){
                    id = this.id
                    takeSnapshot(id)
                }
            }
        });
    })();
</script>

/**
 * Copyright 2013, 2016 IBM Corp.
 *
 * Licensed under the Apache License, Version 2.0 (the 'License');
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an 'AS IS' BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 **/

var bodyParser = require('body-parser')

module.exports = function (RED) {

  function Node (config) {
    RED.nodes.createNode(this, config);
    var node = this;
    var requestSize = '50mb';


    RED.httpAdmin.get('/node-red-camera/status', function (req, res) {
      var n = RED.nodes.getNode(req.query.id)
      var status = {};
      if ('true' == req.query.status) {
        status = {fill:'red', shape:'dot', text:'taking picture...'}
      }
      if (n) {
        n.status(status);
      }
      res.json({});
    });


    RED.httpAdmin.post('/node-red-camera/:id', bodyParser.raw({ type: '*/*', limit: requestSize }), function(req,res) {

        var node = RED.nodes.getNode(req.params.id)

        if (node != null) {
            try {
                node.receive({payload: req.body})
                node.status({})
                res.sendStatus(200)
            } catch(err) {
                node.status({fill:'red', shape:'dot', text:'upload failed'});
                res.sendStatus(500)
                node.error(RED._("upload-camera.failed", { error: err.toString() }))
            }
        } else {
            res.status(404).send("no node found")
        }
    })

    this.on('input', function (msg) {
      if(msg.payload !== '') {
        node.send(msg)
      }
    })
  }
  RED.nodes.registerType('camera', Node)
};

#試したこと
HTML側に記述されているtakeSnapshotメソッドを，Javascript側の this.on('input', function (msg) {...}内に記載すれば良いと考え，HTML側に記載のある関数や変数群をJavascript側に移行しました．

#試した結果
“ReferenceError: navigator is not defined”とのエラーが発生しました

#考えたこと
あまりこの分野について詳しくないのですが，navigatorはWebブラザに関する物のようなので，HTML側のファイルに記載しないと使えないのかなと思いました

#実現したいこと
Javascript側にtakeSnapshotなどの関数を持ってくるとnavigatorに関するエラーが発生するため，Javascript側からHTML側に記載されたtakeSnapshotを叩くことでinputが入ってきたときに写真を撮影する機能を実現したいです．

また，以上のようなことをしないでもうまくtakeSnapshotをinputが入ってきたときに叩く方法があればご教示いただけると幸いです．

よろしくお願いします．