如何从stackdriver nodejs lib获取当前跟踪id和span id

npm install @google-cloud/trace-agent
npm install @opencensus/nodejs

const traceAgent = require('@google-cloud/trace-agent');
const { propagation } = require('@opencensus/core');
const { StackdriverTraceExporter } = require('@opencensus/exporter-stackdriver');

traceAgent.start({ ignoreUrls: [/\/ignore-me/] });

const exporter = new StackdriverTraceExporter({
  projectId: 'YOUR_PROJECT_ID',
});

propagation.setGlobalPropagator(new propagation.B3Format());

const tracing = require('@opencensus/nodejs');
tracing.start({ exporter });

const { tracer } = require('@opencensus/nodejs');

const span = tracer.currentSpan;
const traceId = span ? span.traceId : null;
const spanId = span ? span.id : null;