How to use the blockly.getMainWorkspace function in blockly

constructor(options) {
        options = options || {}

        // if someone is changing the workspace
        this.isCoding = false;
        // if use the strat block
        this.start = options.start === true;
        // set custom highlight
        this.customHighlight = options.customHighlight === true;
        // set the workspace, default is Blockly.getMainWorkspace()
        this.workspace = options.workspace || Blockly.getMainWorkspace();

        this.workspace.addChangeListener((event) => {
            if (event.type == Blockly.Events.BLOCK_MOVE) {
                // update codinge state and remove block highlight
                if (!this.isCoding) this.removeHighlight();
                this.isCoding = true;
            }
        });

        this.reset();
    }

var startup = function(opt_workspace, callback) {
  var workspace = opt_workspace || Blockly.getMainWorkspace();
  // An href with #key trigers an AJAX call to retrieve saved blocks.
  if (window.location.hash.length > 1) {
    retrieveXml(window.location.hash.substring(1), workspace, callback);
  } else {
    monitorChanges_(workspace);
    if (Blockly.Events.isEnabled()) {
      var newEvent = new Blockly.Events.Abstract(null);
      newEvent.type = "new-workspace";
      newEvent.workspaceId = workspace.id;
      Blockly.Events.fire(newEvent);
    }
    if (_.isFunction(callback))
      callback();
  }
};

var restoreBlocks = function(opt_workspace) {
  var url = window.location.href.split('#')[0];
  if ('localStorage' in window && window.localStorage[url]) {
    var workspace = opt_workspace || Blockly.getMainWorkspace();
    var xml = Blockly.Xml.textToDom(window.localStorage[url]);
    Blockly.Xml.domToWorkspace(xml, workspace);
  }
};

var retrieveXml = function(key, opt_workspace, callback) {
  MessageDisplay.alert("Loading Saved Workspace...");
  var workspace = opt_workspace || Blockly.getMainWorkspace();
  urlFromKey_(key, function(url) {
    makeRequest_({
      headers: {Accept: "text/xml"},
      dataType: "text",
      method: "GET",
      url: url,
      success: function(data) {
        if (!data.length) {
          MessageDisplay.alert(HASH_ERROR.replace('%1', window.location.hash), 'error');
          if (_.isFunction(callback))
            callback('Unknown error');
        } else {
          if (Blockly.Events.isEnabled()) {
            Blockly.Events.setGroup(true);
            var loadEvent = new Blockly.Events.Abstract(null);
            loadEvent.type = "load-snapshot";

var linkGist = function(opt_workspace, callback) {
  MessageDisplay.alert("Saving Workspace as Gist on GitHub...");
  var workspace = opt_workspace || Blockly.getMainWorkspace();
  var xml = Blockly.Xml.workspaceToDom(workspace);
  var data = Blockly.Xml.domToPrettyText(xml);
  var testState = TestBlocks && TestBlocks.getState();
  var metaData = _.extend(
    {
      generator: "SparqlBlocks",
      version: packageJson.version,
      baseURI: location.href,
      timestamp: $.now(),
      workspaceXmlFile: "workspace.xml"
    },
    workspace.eventStack ? {
      eventHistoryFile: "eventHistory.json"
    } : {},
    testState ? {
      testStateFile: "testState.json"

var backupOnUnload = function(opt_workspace) {
  var workspace = opt_workspace || Blockly.getMainWorkspace();
  window.addEventListener('unload',
      function() {backupBlocks_(workspace);}, false);
};