react-query/es/core/subscribable.js

Hooks for managing, caching and syncing asynchronous and remote data in React

export var Subscribable = /*#__PURE__*/function () {
  function Subscribable() {
    this.listeners = [];
  }

  var _proto = Subscribable.prototype;

  _proto.subscribe = function subscribe(listener) {
    var _this = this;

    var callback = listener || function () {
      return undefined;
    };

    this.listeners.push(callback);
    this.onSubscribe();
    return function () {
      _this.listeners = _this.listeners.filter(function (x) {
        return x !== callback;
      });

      _this.onUnsubscribe();
    };
  };

  _proto.hasListeners = function hasListeners() {
    return this.listeners.length > 0;
  };

  _proto.onSubscribe = function onSubscribe() {// Do nothing
  };

  _proto.onUnsubscribe = function onUnsubscribe() {// Do nothing
  };

  return Subscribable;
}();