I'm working with datatables.js library. The contents of the code isn't what I'm trying to understand, but how functions work as arguments/parameters. Why doesn't the last version work, whereas the first two do? I understand that the first two are essentially the same thing, but what about javascript prevents me from do the last option below?

function GetDateTime(value){
    if (value == null) return "";
    var pattern = /Date\(([^)]+)\)/; //date format from server side
    var results = pattern.exec(value);
    var dt = new Date(parseFloat(results[1]));
    var tMonth = dt.getMonth() + 1;
    var tDay = dt.getDate();
    
    return (tMonth.toString().length > 1 ? tMonth : "0" + tMonth) + "/" + (tDay.toString().length > 1 ? tDay : "0" + tDay) + "/" + dt.getFullYear();
} // function GetDateTime



...
// This works
{
    "data": "Date",
    "autoWidth": true,
    "render": function (value) {
        return GetDateTime(value);
    }    
}
...
// This works
{
    "data": "Date",
    "autoWidth": true,
    "render": function (value) {
        // The exact same code in GetDateTime(value)
    }    
}
... 
// This does not work
{
    "data": "Date",
    "autoWidth": true,
    "render": GetDateTime(value)
    }    
}

As far as I'm aware, the last one is doing the exact same thing, however when I do that, it throws an error saying "value is undefined." How is value any more defined than with the anonymous function declaration? What about that causes javascript to pass a value in there as opposed to inside an implicit function call?