I know this was a while ago, but it seems shadows on fabric.Group objects is not possible, only on individual objects. Instead why not apply the shadow on the object that forms the background. So in this case it would be:
var newCanvas = new fabric.Canvas('c', {
isDrawingMode: false
});
newCanvas.setWidth(460);
newCanvas.setHeight(365);
var circle = new fabric.Circle({
radius: 100,
fill: '#990000',
originX: 'center',
originY: 'center',
shadow: 'rgba(0,0,0,0.4) 5px 5px 7px'
});
var circle2 = new fabric.Circle({
radius: 50,
fill: '#000000',
originX: 'center',
originY: 'center',
});
var group = new fabric.Group([circle, circle2], {
originX: 'center',
originY: 'center',
left: 225,
top: 185
});
newCanvas.add(group);
newCanvas.renderAll();
* {
box-sizing: border-box;
}
canvas {
border: 1px solid #000000;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/fabric.js/1.4.8/fabric.min.js"></script>
<body>
<div>
<canvas id="c"></canvas>
</div>
</body>