echo'd PHP encode JSON called via AJAX returns what exactly?

Question

I think I'm missing something here:

Using AjAX I get some data from a database and send it back in JSON format $jsondata = array();

while ($Row = mysql_fetch_array($params))
{

    $jsondata[]= array('cat_id'=>$Row["cat_id"], 
                          'category'=>$Row["category"], 
                     'category_desc'=>$Row["category_desc"],
                     'cat_bgd_col'=>$Row["cat_bgd_col"]);
};

echo("{\"Categories\": ".json_encode($jsondata)."};");

No problem so far I think.

On the cleint side I receive back the above into

ajaxRequest.responseText

and if I do this

var categoriesObject = ajaxRequest.responseText; 
alert(categoriesObject);

I see what I expect to see ie the entire array in the alert.

Where it all goes wrong is trying to access the response. The error I get is that the "categoriesObject" is not an object - if not what is it? what's bugginh me is that I can't even access it like this:

document.write(categoriesObject.Categories[0].category);

so what am I doing wrong?

You need to parse the string into an object. Either using eval() which is problematic, or using a JSON parser. See here: http://www.json.org/js.html Side note, frameworks like jQuery have this built in — Pekka, Jan 30 '11 at 22:45

score 11 · Accepted Answer · answered Jan 30 '11 at 22:45

11

You should not create JSON manually. Use:
```
echo json_encode(array('Categories' => $jsondata));
```
or just
```
echo json_encode($jsondata);
```
I don't see a reason to add Categories.
You have to decode the JSON on the client side, using JSON.parse (available in most browsers, but also available as script):
```
var data = JSON.parse(ajaxRequest.responseText);
```
If you want to be very correct, add
```
header('Content-type: application/json');
```
to your PHP script.

answered Jan 30 '11 at 22:45

Felix Kling

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Very nice, covering all aspects. +1 – Pekka Jan 30 '11 at 23:03
The reason I used Categories is that ultimately I'm going to have several arrays in the data. also I did not provide the full php, but just for info you are very correct ! I was using header( "Content-type: text/javascript" ); not that it actually affects the data as far as I can see. – T9b Jan 30 '11 at 23:12

score 2 · Answer 2 · answered Jan 30 '11 at 22:45

2

Are you acutally parsing the JSON? It won't work without.

var categoriesObject = JSON.parse(ajaxRequest.responseText);

answered Jan 30 '11 at 22:45

svens

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Thanks - same as the previous answer but I can't select both - sorry! – T9b Jan 30 '11 at 23:15

echo'd PHP encode JSON called via AJAX returns what exactly?

2 Answers2

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