Don't try to make the string yourself - javascript isn't actually expecting a string; it wants an encoded array or object. Given that, instead of concatenating a string and then finding a way to remove the final comma in order to return said string (let alone escaping and other things you'd need to deal with), make your life easier by building a simple PHP array in your while loop and then json_encode that array when you echo it. In javascript you can then JSON.parse() the returned value and use it.