Make an eventing system mix-in that adds .trigger() and .on() to any input object.

Example usage:

var obj = mixEvents({ name: 'Alice', age: 30 });

obj.on('ageChange', function(){
  console.log('Age changed');
});

obj.age++;

obj.trigger('ageChange'); // This should call our callback!

Should log 'age changed'

Caveats:

• mixEvents should return the original object it was passed after extending it.
• If we repeatedly call .on with the same event name, it should continue to call the old function as well. That is to say, we can have multiple listeners for an event.
• If obj.trigger is called with additional arguments, pass those to the listeners.

• It is not necessary to write a way to remove listeners.

  var mixEvents = function(obj) {
    var events = {};
  
    obj.on = function (event, callback) {
      if (!events[event]) {
        events[event] = [callback];
      } else {
        events[event].push(callback);
      }
    };
  
    obj.trigger = function (event) {
      var args = Array.prototype.slice.call(arguments, 1);
      if (events[event]) {
        events[event].forEach(function (cb) {
          cb.apply(null, args));
        });
      }
    };
  
    return obj;
  };