JSON.parse error when writing data to MySQL database

[d-bohn]

Hello,

I am trying to write my data to a MySQL database following the suggested instructions on the website. My php files and js file are identical to the ones on the website, however, when I run the experiment on the server, I get the following error:

Uncaught SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSON data

A few other things I should note: First, my experiment is bundled into a single file app.js (though I don't think this should matter). Second, the MySQL database I am trying to write to is hosted on a different server, however, the configuration options in database_config.php reflect this, and I have confirmed that I can remote access the database server. Lastly, I have already created a table on the database server with the columns of interest from the experiment output (as per the comments on the website detailing how to save data to MySQL databases.

I am new to php, so any help would be appreciated! Thanks!

[d-bohn]

OK, so after much debugging, I can now write individual trials to the remote database using the saveData MySQL function with on_finish after each trial. However, if I try to save all of the data at the end of the experiment I get a similar JSON.parse error:

Uncaught SyntaxError: JSON.parse: unexpected character at line 1 column 31 of the JSON data

The weird thing is that it will write one row to the database (the very first trial), but then nothing after that.

EDIT:
I should note that there are not even 31 variables being written out to the database, or in the experiment at all (confirmed with jsPsych.data.displayData("csv") at the end of the experiment).

[d-bohn]

I believe I have it figured out. The issue was a combination of the database expecting an integer value and for some reason the one of the html-keyboard-response trials recording keyboard responses. Still not sure where "column 31" came from, though.

[holgerMitterer]

I also got the parse error message, and realized that it is actually not caused by writing to the databse, but by the feedback returned to javascript. I was using the code as it is on the website, (I learned that the 200 status means the query has finished)
//from the save2Database function in javascript
if(xhr.status == 200){
var response = JSON.parse(xhr.responseText);
console.log(response.success);
}

and changed it into this, and now thinks work
if(xhr.status == 200){
var response = xhr.responseText;
console.log(response);
}

the output io console.log from this is {"success": true}, and I don't understand why this is not JSON parsable, but as long as it works ....