'SyntaxError：意外的输入结束'。 解析JSON时出错？

I've got this AJAX function:

function fetchSocialCount(type,fileSrc){
    var count = null;
    var req = new XMLHttpRequest();
    req.onload = function(){
        if(req.status === 200 && req.readyState === 4){
            console.log(req.responseText);
            count = JSON.parse(req.responseText);
        }
    }
    req.open("GET","../scripts/php/returnSocialCount.php?type=" + type + "&fileSrc=" + fileSrc,false);
    req.send();
    if(count !== null){
        return count;
    }
    else{
        console.log("The AJAX request has failed.");
    }
}

But when I run it, I get a 'SyntaxError: Unexpected end of input'. error. The Chrome Dev Tools also covers the count = JSON.parse(req.responseText); part in blue, so I'm guessing it's something wrong with the JSON I'm recieving. From the PHP script, I'm sending a pretty complex JSON object, so I tried to send a really basic one and it worked without problems.

This is the part of the PHP script that sends the response:

echo '{"likes":'.$json->videoListArray[$i]->likes . ',"dislikes":' . $json->videoListArray[$i]->dislikes . '}';

Is there something wrong with the syntax of the echo? What's the problem?

Thanks.

It appears that there is probably a syntax error in your JSON that you're returning. It's not usually a good idea to manually create JSON for this very reason. Try creating an associative array and then use json_encode() to return the desired data to the ajax call:

// Create the array
$data = array();

// Add the data
$data['likes'] = $json->videoListArray[$i]->likes;
$data['dislikes'] = $json->videoListArray[$i]->dislikes;

// Generate JSON from the array and return the desired results
echo json_encode($data);

Reference Documentation:

You need to use json_encode (PHP json_encode manual page) and echo it like so:

echo json_encode(array('likes'=>$json->videoListArray[$i]->likes, 'dislikes'=>$json->videoListArray[$i]->dislikes));

My guess is you have a comma, semi-colon, or some other character in your response that is causing the issue. json_encode will make sure everything is formatted nicely.

EDIT - War10ck beat me to the punch.