How to use the @opentelemetry/core.getTracer function in @opentelemetry/core

const opentelemetry = require('@opentelemetry/core');
const config = require('./setup');

/**
 * The trace instance needs to be initialized first, if you want to enable
 * automatic tracing for built-in plugins (gRPC in this case).
 */
config.setupTracerAndExporters('grpc-client-service');

const grpc = require('grpc');

const messages = require('./helloworld_pb');
const services = require('./helloworld_grpc_pb');
const PORT = 50051;
const tracer = opentelemetry.getTracer();

/** A function which makes requests and handles response. */
function main() {
  // span corresponds to outgoing requests. Here, we have manually created
  // the span, which is created to track work that happens outside of the
  // request lifecycle entirely.
  const span = tracer.startSpan('client.js:main()');
  tracer.withSpan(span, () => {
    console.log('Client traceId ', span.context().traceId);
    const client = new services.GreeterClient(
      `localhost:${PORT}`,
      grpc.credentials.createInsecure()
    );
    const request = new messages.HelloRequest();
    let user;
    if (process.argv.length >= 3) {

'use strict';

const opentelemetry = require('@opentelemetry/core');
const config = require('./setup');

/**
 * The trace instance needs to be initialized first, if you want to enable
 * automatic tracing for built-in plugins (HTTP in this case).
 */
config.setupTracerAndExporters('http-client-service');

const http = require('http');
const tracer = opentelemetry.getTracer();

/** A function which makes requests and handles response. */
function makeRequest() {
    // span corresponds to outgoing requests. Here, we have manually created
    // the span, which is created to track work that happens outside of the
    // request lifecycle entirely.
    const span = tracer.startSpan('makeRequest');
    tracer.withSpan(span, () => {
        http.get({
            host: 'localhost',
            port: 8080,
            path: '/helloworld'
        }, (response) => {
            let body = [];
            response.on('data', chunk => body.push(chunk));
            response.on('end', () => {

function doWork(parent) {
  // Start another span. In this example, the main method already started a
  // span, so that'll be the parent span, and this will be a child span.
  const span = opentelemetry.getTracer().startSpan('doWork', {
    parent: parent
  });

  // simulate some random work.
  for (let i = 0; i <= Math.floor(Math.random() * 40000000); i++) { }

  // Set attributes to the span.
  span.setAttribute('key', 'value');

  // Annotate our span to capture metadata about our operation
  span.addEvent('invoking doWork').end();
}

function doWork(parent) {
  // Start another span. In this example, the main method already started a
  // span, so that'll be the parent span, and this will be a child span.
  const span = opentelemetry.getTracer().startSpan('doWork', {
    parent: parent
  });

  // simulate some random work.
  for (let i = 0; i <= Math.floor(Math.random() * 40000000); i++) { }

  // Set attributes to the span.
  span.setAttribute('key', 'value');

  // Annotate our span to capture metadata about our operation
  span.addEvent('invoking doWork').end();
}