Transformation using Proj4JS

HTML

<script src="http://rawgithub.com/kartena/Proj4Leaflet/master/lib/proj4-compressed.js"></script>
<script src="http://cdnjs.cloudflare.com/ajax/libs/proj4js/2.2.2/proj4.js"></script>
<div id="output"></div>

JavaScript

var wgs84 = "+proj=longlat +datum=WGS84 +no_defs";
        var gda94 = "+proj=lcc +lat_1=-30.75 +lat_2=-35.75 +lat_0=-33.25 +lon_0=147 +x_0=9300000 +y_0=4500000 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs";
        var utm56 = "+proj=utm +zone=56 +south +ellps=WGS84 +datum=WGS84 +units=m +no_defs";
        var NW = [16754886.017653495,-3913048.365375549];
            var SE = [9769428.784424312, 4544185.554848028];

    console.log(proj4(gda94,wgs84,[NW[0], NW[1]]));