Javascript Create JSON Hash Array for jQuery AJAX

I am desperately trying to manually create a JSON-style array in Javascript to send over the network via jQuery's AJAX method.

var fieldsobj = {fields:[]}
$(".fact_field", fact).each(function(index, field){
    var index  = $(field).attr("data-index");
    var name  = $(".fact_field_label", field).text().trim();
    var value  = $(".fact_field_value", field).text().trim();
    fieldsobj["fields"].push({index:index, name:name, value:value});
});
//...
$.ajax({
    type: 'PUT',
    url: url,
    data: fieldsobj,
    success: function(data){...
    },
    complete: function(){...
    }
});

What I want is the following:

{fields => [{index:0, name:1, value:2},{...},{...}]}

What I get is this:

 {"fields"=>{"0"=>{...}, "1"=>{..}, "2"=>{...}, "3"=>{...}}

What am I doing wrong?