How to use the jaeger-client.initTracerFromEnv function in jaeger-client

import * as jaegerClient from "jaeger-client";
import * as promClient from "prom-client";
import * as opentracing from "opentracing";

const tracingConfig: jaegerClient.TracingConfig = {};
const tracingOptions: jaegerClient.TracingOptions = {};

const tracer = jaegerClient.initTracer(tracingConfig, tracingOptions);
jaegerClient.initTracerFromEnv(tracingConfig, tracingOptions);

const metrics = new jaegerClient.PrometheusMetricsFactory(promClient, "foo");

const textCodec = new jaegerClient.TextMapCodec({
    contextKey: 'trace-id',
    baggagePrefix: 'baggage-',
    urlEncoding: false,
});
tracer.registerInjector(opentracing.FORMAT_TEXT_MAP, textCodec);
tracer.registerExtractor(opentracing.FORMAT_TEXT_MAP, textCodec);

const zipkinB3TextMapCodec = new jaegerClient.ZipkinB3TextMapCodec({
    baggagePrefix: 'baggage-',
    urlEncoding: false,
});
tracer.registerInjector(opentracing.FORMAT_HTTP_HEADERS, zipkinB3TextMapCodec);

/** Whether or not to enable Jaeger. */
        useJaeger: boolean
        /** The access token for lightstep tracing. */
        lightstepAccessToken: string
    }
): Tracer | undefined {
    if (useJaeger) {
        const config = {
            serviceName,
            sampler: {
                type: 'const',
                param: 1,
            },
        }

        return initTracerFromEnv(config, {})
    }

    if (lightstepAccessToken !== '') {
        return new lightstep.Tracer({
            access_token: lightstepAccessToken,
            component_name: serviceName,
        })
    }

    return undefined
}