显示jquery ui“instance”方法的键和值

如何显示jQuery实例的所有键和值。我写了这段代码但没用。

html格式:

<input id="a" type="text">

查询:

$(function() {
    $("#a").autocomplete({
       source:["abc","def","ghi"]
    });

    var t="<div class='show'>";
    $.each($("#a").autocomplete( "instance" ),function(key,value){
       t+= key +" = " + value + "</br>";
    });
    t+="</div>";

    $("body").append(t); 
});

这个错误 jquery-1.10.2.js:516 Uncaught Error: no such method 'instance' for autocomplete widget instance