如何将参数发送到远程文件

I've script like this

$(function(){
    //attach autocomplete  
    $("#user_key").autocomplete({
            //define callback to format results  
                source: function(req, add){
                    //pass request to server  
                    $.getJSON("/ajax/user_autocomplete.php?user_key=?",req, function(data){
                        //create array for response objects
                        var suggestions = [];
                        //process response
                        $.each(data, function(i, val){
                        suggestions.push(val.name);  
                    });
                    //pass array to callback
                add(suggestions);
            });
        }
    });
});

and want to send one param to php file for receiving answer , how can I do it within this script ? and is it neccessary to have in html for method="get" or doen't it matter ?

I've to write {param: $(this).val} instead of req or how ?

The req argument will be a object containing the attribute term. This, and any other GET parameters, will need to be defined for the second argument for $.getJSON

function(req, add){
                var params = {
                    user_key: myUserKeyVar,
                    term : req.term,
                    otherKey: myOtherKey
                };
                //pass request to server  
                $.getJSON("/ajax/user_autocomplete.php",params, function(data){
                    //create array for response objects
                    var suggestions = [];
                    //process response
                    $.each(data, function(i, val){
                    suggestions.push(val.name);  
                });
                //pass array to callback
            add(suggestions);

Just do:

       $('#user_key').autocomplete(
        {
            source: '/ajax/user_autocomplete.php'
        });

As long as you send back correct JSON from user_autocomplete.php then all is good.