trace context

// producer

import * as traceparent from 'tctx/traceparent';
import * as tracestate from 'tctx/tracestate';

fetch('/api', {
    headers: {
        traceparent: traceparent.make(),
        tracestate: tracestate.make({ key: 'value' }),
    },
});

// consumer

import * as traceparent from 'tctx/traceparent';
import * as tracestate from 'tctx/tracestate';

const parent_key = traceparent.parse(request.headers.traceparent);
const parent_state = tracestate.parse(request.headers.tracestate);
parent_state.set('vendor', 'value');

fetch('/downstream', {
    headers: {
        traceparent: parent.child(),
        tracestate: parent_state,
    },
});