ajax with JavaScript exception: unexpected end of input - php

Question

I have an input field for a concept and when the user fills it out, he has to then check if the concept exists. So I made a check button, which checks a database using ajax and JavaScript to see if the concept exists. My problem is when using ajax and JavaScript I get this exception:
unexpected end of input
JS :
var concept = document.getElementById('acConceptName').value;
xmlhttp = new XMLHttpRequest();
xmlhttp.onreadystatechange=function(){
if(xmlhttp.readyState==4 && xmlhttp.status==200){
var isexisted = JSON.parse(xmlhttp.responseText);
if(isexisted[0]==true){
var errorMessage = document.getElementById('acSuggesConcepts');
var p = document.createElement('p');
p.innerHTML="this concept is already existed";
errorMessage.appendChild(p);
errorMessage.style.display="block";
}
}
}
xmlhttp.open("GET","http://localhost/Mar7ba/Ontology/isExistedConcept/"+concept+"/TRUE",true);
xmlhttp.send();
What is the exception and how can I solve it ?
PHP : function to check database and I always return true in it
public function isExistedConcept($concpetName,$Ajax){
if($Ajax==true){
$results=true
$d=array($results);
return json_encode($d);
}
}
Demo: http://jsfiddle.net/Wiliam_Kinaan/s7Srx/2/

Answer 1

After looking at the code for a while, one thing that might be a suspect is your PHP.
Your function in php ends with a return command. What the AJAX call is actually waiting for is some data to be sent back. The return command simply passes that value back to the entity that originally called the function.
Try alter your function to echo the result as opposed to returning it. Save your return value for when you need the result to go into another PHP function, not when you are returning data to the client.
I only put this return command here for readability.
public function isExistedConcept($concpetName,$Ajax){
if($Ajax==true){
$results=true
$d=array($results);
echo json_encode($d);
}
return;
}

Answer 2

Try this:
public function isExistedConcept($concpetName,$Ajax) {
if( $Ajax) return "1";
}
// This is a simplified version of what you're doing, but it returns "1" instead of "[true]"
// Now for the JS:
if( xmlhttp.readyState == 4 && xmlhttp.status == 200) {
var isexisted = xmlhttp.responseText == "1";
if( isexisted) {...}
If that doesn't work, try adding alert(xmlhttp.responseText) and see if you're getting anything other than what should be there.

Answer 3

try this :
var concept = document.getElementById('acConceptName').value;
xmlhttp = new XMLHttpRequest();
xmlhttp.open("GET","http://localhost/Mar7ba/Ontology/isExistedConcept/"+concept+"/TRUE",true);
xmlhttp.onreadystatechange=function(){
if(xmlhttp.readyState==4){
if(xmlhttp.status==200){
var isexisted = JSON.parse(xmlhttp.responseText);
if(isexisted[0]==true){
var errorMessage = document.getElementById('acSuggesConcepts');
var p = document.createElement('p');
p.innerHTML="this concept is already existed";
errorMessage.appendChild(p);
errorMessage.style.display="block";
}
else{
console.log('error');
}
}
}
}
xmlhttp.send(null);