MySQL select result inside JS function

Question

I found a simple JS script that works as a chatbot. in the script itself the results of lastUserMessage are predefined inline like

if (lastUserMessage === 'name') {
   botMessage = 'My name is ' + botName;
}

What I am trying to achieve is if the JS to search for lastUserMessage within a db and to provide botMessage from there.

I am sure it should't be that hard, but I cant figure out how to do it.

Here is the JS code:

nlp = window.nlp_compromise;
var messages = [], //array that hold the record of each string in chat
  lastUserMessage = "", //keeps track of the most recent input string from the user
  botMessage = "", //var keeps track of what the chatbot is going to say
  botName = 'Bot Name', //name of the chatbot
  talking = true; //when false the speach function doesn't work

//edit this function to change what the chatbot says
function chatbotResponse() {
  talking = true;
  botMessage = "Ops... didn't get this"; //the default message

  if (lastUserMessage === 'name') {
    botMessage = 'My name is ' + botName;
  }

}

//this runs each time enter is pressed.
//It controls the overall input and output
function newEntry() {
  //if the message from the user isn't empty then run 
  if (document.getElementById("chatbox").value != "") {
    //pulls the value from the chatbox ands sets it to lastUserMessage
    lastUserMessage = document.getElementById("chatbox").value;
    //sets the chat box to be clear
    document.getElementById("chatbox").value = "";
    //adds the value of the chatbox to the array messages
    messages.push(lastUserMessage);
    //Speech(lastUserMessage);  //says what the user typed outloud
    //sets the variable botMessage in response to lastUserMessage
    chatbotResponse();
    //add the chatbot's name and message to the array messages
    messages.push("<b>" + botName + ":</b> " + botMessage);
    // says the message using the text to speech function written below
    Speech(botMessage);
    //outputs the last few array elements of messages to html
    for (var i = 1; i < 8; i++) {
      if (messages[messages.length - i])
        document.getElementById("chatlog" + i).innerHTML = messages[messages.length - i];
    }
  }
}

//runs the keypress() function when a key is pressed
document.onkeypress = keyPress;
//if the key pressed is 'enter' runs the function newEntry()
function keyPress(e) {
  var x = e || window.event;
  var key = (x.keyCode || x.which);
  if (key == 13 || key == 3) {
    //runs this function when enter is pressed
    newEntry();
  }
  if (key == 38) {
    console.log('hi')
      //document.getElementById("chatbox").value = lastUserMessage;
  }
}

//clears the placeholder text ion the chatbox
//this function is set to run when the users brings focus to the chatbox, by clicking on it
function placeHolder() {
  document.getElementById("chatbox").placeholder = "";
}

Here is the HTML code

<div id='bodybox'>
  <div id='chatborder'>
    <p id="chatlog2" class="chatlog">&nbsp;</p>
    <p id="chatlog1" class="chatlog">&nbsp;</p>
    <input type="text" name="chat" id="chatbox" placeholder="Hi there! Type here to talk to me." onfocus="placeHolder()">
  </div>

What need to happen?

Ideally, the script should take the values "lastUserMessage" and "botMessage" from a db that has 2 columns "lastUserMessage" and "botMessage".

What I tried to to do is following Ghost's comment below... but didn't work.

    nlp = window.nlp_compromise;
var messages = [], //array that hold the record of each string in chat
  lastUserMessage = "", //keeps track of the most recent input string from the user
  botMessage = "", //var keeps track of what the chatbot is going to say
  botName = 'Bot Name', //name of the chatbot
  talking = true; //when false the speach function doesn't work

//edit this function to change what the chatbot says
function chatbotResponse() {
  talking = true;
  botMessage = "Ops... didn't get this"; //the default message

      $.ajax({                                      
  url: 'db_query.php',         
  data: "lastUserMessag=lastUserMessag", 
  dataType: 'json',                 
  success: function(data)          
  {
    var lastUserMessage_db = data[0]; 
    var botMessage_db= data[1];

if (lastUserMessage === lastUserMessage_db) {
    botMessage = botMessage_db;
  }
  } 
});

}

//this runs each time enter is pressed.
//It controls the overall input and output
function newEntry() {
  //if the message from the user isn't empty then run 
  if (document.getElementById("chatbox").value != "") {
    //pulls the value from the chatbox ands sets it to lastUserMessage
    lastUserMessage = document.getElementById("chatbox").value;
    //sets the chat box to be clear
    document.getElementById("chatbox").value = "";
    //adds the value of the chatbox to the array messages
    messages.push(lastUserMessage);
    //Speech(lastUserMessage);  //says what the user typed outloud
    //sets the variable botMessage in response to lastUserMessage
    chatbotResponse();
    //add the chatbot's name and message to the array messages
    messages.push("<b>" + botName + ":</b> " + botMessage);
    // says the message using the text to speech function written below
    Speech(botMessage);
    //outputs the last few array elements of messages to html
    for (var i = 1; i < 8; i++) {
      if (messages[messages.length - i])
        document.getElementById("chatlog" + i).innerHTML = messages[messages.length - i];
    }
  }
}

//runs the keypress() function when a key is pressed
document.onkeypress = keyPress;
//if the key pressed is 'enter' runs the function newEntry()
function keyPress(e) {
  var x = e || window.event;
  var key = (x.keyCode || x.which);
  if (key == 13 || key == 3) {
    //runs this function when enter is pressed
    newEntry();
  }
  if (key == 38) {
    console.log('hi')
      //document.getElementById("chatbox").value = lastUserMessage;
  }
}

//clears the placeholder text ion the chatbox
//this function is set to run when the users brings focus to the chatbox, by clicking on it
function placeHolder() {
  document.getElementById("chatbox").placeholder = "";
}

And in DB_query.php I have

$p = $_GET['lastUserMessag']; 
      $query=mysql_query("SELECT lastUserMessag, botMessage FROM `aiml` WHERE lastUserMessag='$p'");
      $array = mysql_fetch_row($query);  
    echo json_encode($array);