readmongo/node_modules/event-pubsub/event-pubsub-browser.js

'use strict';

window.EventPubSub=class EventPubSub {
  constructor( scope ) {
      this._events_ = {};
      this.publish = this.trigger = this.emit;
      this.subscribe = this.on;
      this.unSubscribe = this.off;
  }

  on( type, handler, once ) {
      if ( !handler ) {
          throw new ReferenceError( 'handler not defined.' );
      }

      if ( !this._events_[ type ] ) {
          this._events_[ type ] = [];
      }

       if(once){
          handler._once_ = once;
      }

      this._events_[ type ].push( handler );
      return this;
  }

  once( type, handler ) {
      return this.on( type, handler, true );
  }

  off( type, handler ) {
      if ( !this._events_[ type ] ) {
          return this;
      }

      if ( !handler ) {
          throw new ReferenceError( 'handler not defined. if you wish to remove all handlers from the event please pass "*" as the handler' );
      }

      if ( handler == '*' ) {
          delete this._events_[ type ];
          return this;
      }

      const handlers = this._events_[ type ];

      while ( handlers.includes( handler ) ) {
          handlers.splice(
              handlers.indexOf( handler ),
              1
          );
      }

      if ( handlers.length < 1 ) {
          delete this._events_[ type ];
      }

      return this;
  }

  emit( type, ...args ) {
      if ( !this._events_[ type ] ) {
          return this.emit$( type, ...args );
      }

      const handlers = this._events_[ type ];
      const onceHandled=[];

      for ( let handler of handlers ) {
          handler.apply( this, args );
          if(handler._once_){
            onceHandled.push(handler);
          }
      }

      for(let handler of onceHandled){
        this.off(type,handler);
      }

      return this.emit$( type, ...args );
  }

  emit$( type, ...args ) {
      if ( !this._events_[ '*' ] ) {
          return this;
      }

      const catchAll = this._events_[ '*' ];

      for ( let handler of catchAll ) {
          handler.call( this, type, ...args );
      }

      return this;
  }
}

if (!Array.prototype.includes) {
  Array.prototype.includes = function(searchElement /*, fromIndex*/) {
    'use strict';
    if (this == null) {
      throw new TypeError('Array.prototype.includes called on null or undefined');
    }

    var O = Object(this);
    var len = parseInt(O.length, 10) || 0;
    if (len === 0) {
      return false;
    }
    var n = parseInt(arguments[1], 10) || 0;
    var k;
    if (n >= 0) {
      k = n;
    } else {
      k = len + n;
      if (k < 0) {k = 0;}
    }
    var currentElement;
    while (k < len) {
      currentElement = O[k];
      if (searchElement === currentElement ||
         (searchElement !== searchElement && currentElement !== currentElement)) { // NaN !== NaN
        return true;
      }
      k++;
    }
    return false;
  };
}