There are two main entrypoints: campaigning via Election.campaign, and observing the leader via Election.observe.

see

https://github.com/etcd-io/etcd/blob/master/client/v3/concurrency/election.go

example

const os = require('os');
const client = new Etcd3();
const election = client.election('singleton-job');

function runCampaign() {
  const campaign = election.campaign(os.hostname())
  campaign.on('elected', () => {
    // This server is now the leader! Let's start doing work
    doSomeWork();
  });
  campaign.on('error', error => {
    // An error happened that caused our campaign to fail. If we were the
    // leader, make sure to stop doing work (another server is the leader
    // now) and create a new campaign.
    console.error(error);
    stopDoingWork();
    setTimeout(runCampaign, 5000);
  });
}

async function observeLeader() {
  const observer = await election.observe();
  console.log('The current leader is', observer.leader());
  observer.on('change', leader => console.log('The new leader is', leader));
  observer.on('error', () => {
    // Something happened that fatally interrupted observation.
    setTimeout(observeLeader, 5000);
  });
}