Alexa (Expecting 'STRING', 'NUMBER', 'NULL', 'TRUE', 'FALSE', '{', '[', got 'undefined') - json

Question

My code is not working when I test it in Amazon Developer and I don't see anything wrong with my code. It says my response is invalid.
Here's the code I tried to run but failed(I ran one response but not the other):
var Alexa = require('alexa-sdk');
exports.handler = function(event, context, callback) {
var alexa = Alexa.handler(event, context);
// alexa.dynamoDBTableName = 'YourTableName'; // creates new table for userid:session.attributes
alexa.registerHandlers(handlers);
alexa.execute();
};
var handlers = {
'LaunchRequest': function () {
this.emit('WelcomeIntent');
},
'WelcomeIntent': function () {
this.emit(':ask', 'Welcome to the guessing game! What difficulty would you like to play? Easy, Medium, or Hard?');
},
//------------------------------------------------------------------------------------------------------------------------------------------------
'DifficultyIntent': function (){
var difficulty = this.event.request.intent.slots.difficulty.value;
var range = 10; this.attributes['RandomNumberEnd'] = range;
if (difficulty === 'easy')
{ range = 10;
this.emit[':ask Your range is 1 - ' + range]
}
else if (difficulty === 'medium')
{ range = 100;
this.emit[':ask Your range is 1 - ' + range]
}
else (difficulty === 'hard');
{ range = 1000;
this.emit[':ask Your range is 1 - ' + range]
}
var randomNumber = Math.floor((Math.random()*range)+1);
var rightAnswer = this.attributes['rightAnswer'] = rightAnswer;
}, //check the user's guess with the right answer
'UserGuessIntent': function (){
var guess = this.event.request.intent.slots.guess.value;
this.attributes['guess'] = guess;
this.emit('CheckIntent'); },
'CheckIntent': function (){
var guess = this.attributes['guess'];
this.attributes['rightAnswer'] = randomNumber;
if(guess < rightAnswer){
this.emit(':ask', 'Try Again! Guess higher!');
}
else if(guess > rightAnswer)
{this.emit(':ask', 'Try Again! Guess lower!');
}
else{
this.emit(':tell', 'You are correct! Congratulations!');
}
},
'QuitIntent': function(){
var stop = this.event.request.intent.slots.stop.value;
this.emit('AMAZON.StopIntent');
},
'AMAZON.StopIntent' : function(){
var rightAnswer = this.attributes['rightAnswer'];
this.emit(':tell', 'The right answer is ' + rightAnswer + '. Goodbye!');
}
};