How can I convert this JSON from PHP to a Javascript array

Question

I am trying to assign a json array to a javascript array so that my JS functions can access the array. So I have an ajax call to MySQL db to get a JSON array of data:

var data = [];
    $.ajax({
      type:"post",
      url:"position.php",
      dataType:'json',
      success:function(jsonarray){
                data=$.parseJSON(jsonarray);
               }
     });

position.php:

<?php
include 'dbconnect.php';  

$sql = "SELECT pid, posX, posY FROM posTable;";
$result = $conn->query($sql);
$myrows = $result->num_rows;
$return=array();

if ($result->num_rows>0){

while($row=$result->fetch_assoc()){      
     $return[]=array((int)$row['pid'],(int)$row['posX'],(int)$row['posY']);        
     }

}else{
echo "[]";
}
echo json_encode($return);
$conn->close();
?>

This gives an output like this:

[[1,749,1000],[2,855,986],[3,955,946],[4,1037,934],[5,1111,912]]

And from this I want the following two dimensional array so that I can access its memebers in this form:

data[i][j]

data => [[1,749,1000],[2,855,986],[3,955,946],[4,1037,934],[5,1111,912]]

However when I execute the code I keep getting the following error:

Uncaught SyntaxError: Unexpected token , in JSON at position 1

What am I doing wrong?

score 2 · Accepted Answer · answered Jun 02 '16 at 09:47

2

jQuery will automatically parse a JSON response before populating the success function's first argument.

$.parseJSON(jsonarray); calls toString() on your array and then tries to parse it as JSON, which it isn't (because Array.prototype.toString() doesn't convert to JSON).

Just don't try to parse it again.

answered Jun 02 '16 at 09:47

Quentin

914,110
126
1,211
1,335

I now assigned jsonarray to data without the json parsing and it takes care of the error. How can I see that data is now properly two dimensional? i.e. how can I see that data is truly of the form data[i][j] – Emmanuel N K Jun 02 '16 at 09:54
`console.log` is the usual choice for inspecting an element – Quentin Jun 02 '16 at 09:55
When I try this, I get 0 undefined error: ` for(var i=0;i<2;i++){ for(var j=0;j<3;j++){ alert(data[i][j]); } }` UPDATE: From console I can see that data is indeed a 2D array – Emmanuel N K Jun 02 '16 at 09:56
Are you sure you get an undefined **error** and not just an alert where the value is a stringified `undefined` value? – Quentin Jun 02 '16 at 10:00
I get : **Cannot read property '0' of undefined** Alert does not pop up – Emmanuel N K Jun 02 '16 at 10:02
It's hard to tell without more context. This does seem to be a different problem though, so I suggest that you ask a new question with a http://stackoverflow.com/help/mcve showing how you are running that code and when. – Quentin Jun 02 '16 at 10:04
It now works when I place the for loops inside the ajax call (within the success function). I have no idea why this is yet I defined **data** outside the ajax call. – Emmanuel N K Jun 02 '16 at 10:10
Amazing find and answer, that one! +1 – Emmanuel N K Jun 02 '16 at 10:29

How can I convert this JSON from PHP to a Javascript array

1 Answers1