How to use the browserstack.localIdentifier function in browserstack

import {Capability, Browser} from 'selenium-webdriver';

const capabilities = {
  [Capability.PLATFORM]: 'WINDOWS',
  [Capability.BROWSER_NAME]: Browser.CHROME,
  [Capability.VERSION]: 73,
};

// browserstack specific capabilities - https://www.browserstack.com/automate/capabilities
if (process.env.CI) {
  capabilities['browserstack.local'] = true;
  capabilities['browserstack.localIdentifier'] = process.env.BROWSERSTACK_LOCAL_IDENTIFIER || process.env.TRAVIS_JOB_NUMBER;
  capabilities['browserstack.networkLogs'] = true;
  capabilities.os = 'WINDOWS';
  capabilities.os_version = '10';
  capabilities.browser = Browser.CHROME;
  capabilities.browser_version = '73';
}

export default capabilities;

'#extraCapabilities'() {
        const capabilities: any = { 'browserstack.local': 'true' };
        assert.deepEqual(tunnel.extraCapabilities, capabilities);
        capabilities['browserstack.localIdentifier'] = tunnel.tunnelId = 'foo';
        assert.deepEqual(tunnel.extraCapabilities, capabilities);
      },

'#extraCapabilities'() {
        const capabilities: any = { 'browserstack.local': 'true' };
        assert.deepEqual(tunnel.extraCapabilities, capabilities);
        capabilities['browserstack.localIdentifier'] = tunnel.tunnelId = 'foo';
        assert.deepEqual(tunnel.extraCapabilities, capabilities);
      },

get extraCapabilities(): Object {
    const capabilities: any = {
      'browserstack.local': 'true'
    };

    if (this.tunnelId) {
      capabilities['browserstack.localIdentifier'] = this.tunnelId;
    }

    return capabilities;
  }

var browsers = ALL_BROWSERS.map(function(b) {
    b['browserstack.local'] = 'true';
    b['browserstack.debug'] = 'true';
    b['browserstack.localIdentifier'] = process.env.BROWSERSTACK_LOCAL_IDENTIFIER;
    b['url'] = url;
    return b;
  });