parsing JSON (from an AJAX request) into a table

HTML

<body onLoad="buildHtmlTable()">
    <table id="excelDataTable" border="1"></table>
</body>

CSS

th {
    font-weight : bold
}

JavaScript

json_link = 'https://trello.com/b/aNyUo9P8.json';

// Makes an AJAX request and builds the HTML Table out of the returned JSON data
function buildHtmlTable() {
    $.getJSON(json_link, function (result_data) {
    console.log(result_data);
        var data = result_data.rows;
        var columns = addAllColumnHeaders(data);

        for (var i = 0; i < data.length; i++) {
            var row$ = $('<tr/>');
            for (var colIndex = 0; colIndex < columns.length; colIndex++) {
                var cellValue = data[i][columns[colIndex]];

                if (cellValue == null) {
                    cellValue = "";
                }

                row$.append($('<td/>').html(cellValue));
            }
            $("#excelDataTable").append(row$);
        }
    });
}
// Adds a header row to the table and returns the set of columns.
// Need to do union of keys from all records as some records may not contain
// all records
function addAllColumnHeaders(myList) {
    var columnSet = [];
    var headerTr$ = $('<tr/>');

    for (var i = 0; i < myList.length; i++) {
        var rowHash = myList[i];
        for (var key in rowHash) {
            if ($.inArray(key, columnSet) == -1) {
                columnSet.push(key);
                headerTr$.append($('<th/>').html(key));
            }
        }
    }
    $("#excelDataTable").append(headerTr$);

    return columnSet;
}