const tracing = require('@opencensus/nodejs');
const { StackdriverTraceExporter } = require('@opencensus/exporter-stackdriver');

const exporter = new StackdriverTraceExporter({projectId: "YOUR-GCP-PROJECT"});

const tracer = tracing.registerExporter(exporter).start({ samplingRate: 1 }).tracer();

function A () {
  let traceId;
  tracer.startRootSpan({ name: 'A' }, rootSpan => {
    doSomeWorkInA();

    traceId = rootSpan.traceId();
    rootSpan.end();
  });

  // Pass traceId to another function
}

function B () {
  let traceId = 'The trace ID passed from A';
  tracer.startRootSpan({ name: 'B', traceId: traceId }, rootSpan => {
    doSomeWorkInB();

    rootSpan.end();
  });

  // Keep passing the traceId if needed
}