[jQuery] JSON / PHP's json_encode()

[jQuery] JSON / PHP's json_encode()


Has nothing to do with jQuery directly, but there's alot of really
great developers here, so maybe I'm missing something that someone
else will catch...
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[json.js]
{
    "itemtitle1": function(){
            alert("this is item title 1's callback");
    },
    "itemtitle2": function(){
            alert("this is item title 2");
    }
}
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This works great in Javascript- exactly how I want it
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mainscript.js
$.getJSON("json.js",{},
    function(json) {
        json.itemtitle1(); // fires the alert for itemtitle1
    }
);
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The problem arises when I use the same json.js in my PHP script
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mainpage.php
$json=json_decode(file_get_contents('json.js'),1);
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Note that if I change the function in json.js to a string of text or a
boolean etc., then the php file works fine- for some reason it's not
parsing my javascript function, even though that works [because JSON
is an object, my json.js has a function named itemtitle1. I don't
expect PHP to run or convert my function, but I need to be able to use
json.js in my php script.
Any ideas? Is this invalid JSON, even though it's valid javascript,
or is it json_encode()'s fault?