HTML canvas spotlight effect

Answer 1

this code works for me:

x = event.pageX;
y = event.pageY;
radius = 10;
context = canvas.getContext("2d");

context.fillStyle = "black";
context.fillRect(0, 0, context.canvas.width, context.canvas.height);

context.beginPath();
var radialGradient= context.createRadialGradient(x,y,1,x,y,radius);
radialGradient.addColorStop(0,"rgba(255,255,255,1");
radialGradient.addColorStop(1,"rgba(0,0,0,1)");
//context.globalCompositeOperation = "destination-out";
context.fillStyle = radialGradient; 
context.arc(x, y, radius, 0, Math.PI*2, false);
context.fill();
context.closePath();

it seems that this line was messing it context.globalCompositeOperation = "destination-out";

there were also pointless lines in your code like beginnig path before filling rect and fill() function after filling path