/*
 Given an `other` object that has on/off methods, bind the given `callback` to an event by the given name.
 The `callback` will be called with the `this` context of the object that .listenTo is being called on.
 Can be called:
   .listenTo(other, eventName, callback)
 OR
   .listenTo(other, {
     eventName1: callback1,
     eventName2: callback2
   })
 */
 listenTo(other, arg, callback?) {
   if (typeof arg === 'object') { // given dictionary of callbacks
     for (let eventName in arg) {
       if (arg.hasOwnProperty(eventName)) {
         this.listenTo(other, eventName, arg[eventName])
       }
     }
   } else if (typeof arg === 'string') {
     other.on(
       arg + '.' + this.getListenerNamespace(), // use event namespacing to identify this object
       $.proxy(callback, this) // always use `this` context
         // the usually-undesired jQuery guid behavior doesn't matter,
         // because we always unbind via namespace
     )
   }
 }

 typeahead.lookup = function() {
   this.query = this.$element.val() || '';
   var items = this.source(this.query, $.proxy(this.process, this));
   return items ? this.process(items) : items;
 };