<canvas id="canvas" width="500" height="500"></canvas>

<script>
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");

for (let x = 0; x <=10; x++){
for (let y = 0; y <=10; y++){
ctx.fillStyle = '#' + Math.floor(Math.random()*16777215).toString(16);
let s =  Math.floor(Math.random() * 100);
ctx.fillRect(x*50,y*50, s, s);
}
}

</script>