Shadow - Fabric.js
HTML
<canvas id="c" width="600" height="600"></canvas>
JavaScript
var canvas = new fabric.Canvas('c');
var shadow = {
color: '#000',
blur: 20,
//offsetX: 10,
//offsetY: 10,
//opacity: 0.6,
fillShadow: true,
strokeShadow: true
}
var rect = new fabric.Rect({
left: 20,
top: 20,
fill: null,
stroke: "#000",
width: 300,
height: 300,
strokeWidth: 4,
});
rect.setShadow(shadow);
canvas.add(rect);