src/EventEmitter.js
/**
         * Registers an event handler to fire only once on an event
         * @param event
         * @param listener
         */
Registers an event handler to fire only once on an event
@param event
@param listener
Registers an event handler to fire only once on an event @param event @param listener
once(event, listener) {
            const callback = () => {
                let args = [].slice.call(arguments, 1);
                this.removeListener(event, callback);
                listener.apply(this, args);
            };
            this.on(event, callback);
        }
once ( event , listener ) { const callback = ( ) => { let args = [ ] . slice . call ( arguments , 1 ) ; this . removeListener ( event , callback ) ; listener . apply ( this , args ) ; } ; this . on ( event , callback ) ; }
Registers an event handler to fire only once on an event
 @param event
 @param listener
Registers an event handler to fire only once on an event @param event @param listener