PHP json_encode to Javascript undefined/null

Question

I'm having an issue returning a JSON from PHP to Javascript. Below is my PHP to create the JSON:

$environment[] = array('id' => $env, 'adjacencies' => $hostnames);

foreach($hostnames as $hostname) {
        $environment[] = array('id' => $hostname, 'name' => $hostname, 'data' => array());
    }

return json_encode($environment);;

When I print the json_encode environment to a text file, it comes back as:

[{"id":"Dev","adjacencies":["tb23","tbwag","tbvg","tbut"]},{"id":"tb23","name":"tb23","data":[]},{"id":"tbwag","name":"tbwag","data":[]},{"id":"tbvg","name":"tbvg","data":[]},{"id":"tbut","name":"tbut","data":[]}]

It seems that this is printing out properly but when I return it to the Javascript its coming back as undefined/null. Below is the javascript with the ajax call:

var ajax = new AJAX();
var args = "id=" + $("#apps").val() + "&env=" + node.id + "&nocache=" + (new Date()).valueOf();
ajax.connect("POST", "http://" + window.location.hostname + "/project/graph/host", args, function(json) {

var output = '';
for (property in json) {
    output += property + ': ' + json[property]+'; ';
}
alert(output);
});

I've obviously tried a lot of different things to get it to print out but haven't had any luck. In PHP, I've tried json_last_error and it came back as '0', which means that there isn't an issue with the JSON structure.

In the end, I'd like to use the following command in Javascript to continue building my graph:

var hostNodes = eval('(' + json + ')'); 

Any help is appreciated as to why I can't get this to come back!

Answer 1

Keep your PHP code in an unique file that receives one post parameters, then construct the json array if it set, and at the bottom you can do

echo json_encode($json);
flush();

I'm not a professional with pure javascript and I'm not familar with your approach, but you should consider using jQuery, at least I'm going to suggest one way to receive an json array so that you can easily work with it (you also make sure that the data is json):

$.ajax(
{
    // Post select to url.
    type : 'post',
    url : 'myPHPAjaxHandler.php',
    dataType : 'json',
    data : 
    {
        'select' : true
    },
    success : function(data)
    {
        // PHP has returned a json array.

        var id, hostname;

        for(var i = 0; i < data.length; i++)
        {
            id = data[i].id;
            hostname = hostname[i].id;
            // Construct a string or an object using the data.

        }
    },
    complete : function(data)
    {
        // Optional.
    }
});

Like I say, It's there for you to decide whether you pick it up or not. It can become handy for complex projects.

Answer 2

It looks like you're assuming that the data passed to the callback function will be your JSON already parsed into JS objects, but I don't see any indication that that would be the case; it's most likely the raw JSON data that must be parsed into JS objects using JSON.parse (NOT eval() - eval() is very dangerous, you should always prefer JSON.parse when working with true JSON data, as it will not permit XSS-style attacks as they are generally not "pure" JSON.)