JS - Convert a (nested) JSON object to HTML

For testing purposes I wanted to display the JSON retrieved from an API in a HTML page. I used Fiddler for that, but after some security was included that became impossible. The following Javascript function converts the JSON to a ordered list tree:

function jsonToHtml(data) {
    var result = "<ol>";

    for (var key in data) {
        if (typeof (data[key]) == 'object' && data[key] != null) {
            result += "<li><span class='key'>" + key + "</span>:<ul>";
            result += jsonToHtml(data[key]);
            result += '</ul></li>';
        }
        else {
            result += "<li><span class='key'>" + key + '</span>: ';
            result += '<span class="string">' + data[key] + '</span></li>';
        }
    };

    result += '</ol>';
    return (result);
}