@polkadot/api-provider/mock/subscribe.js

"use strict";

// Copyright 2017-2018 Jaco Greeff
// This software may be modified and distributed under the terms
// of the ISC license. See the LICENSE file for details.
module.exports = async function subscribe(self, method, params) {
  self.l.debug(() => ['subscribe', method, params]);

  if (self.subscriptions[method]) {
    // flowlint-next-line unclear-type:off
    const callback = params.pop();
    const id = ++self.subscriptionId;
    self.subscriptions[method].callbacks[id] = callback;
    self.subscriptionMap[id] = method;
    callback(null, self.subscriptions[method].lastValue);
    return id;
  }

  throw new Error(`provider.subscribe: Invalid method '${method}'`);
};