const canvas = document.getElementById('test');
const context = canvas.getContext('2d');
const blank = document.createElement('canvas');
blank.width = canvas.width;
blank.height = canvas.height;
for (let i = 0; i < Math.floor(Math.random() * 10); ++i) {
context.fillStyle = '#' + Math.floor(Math.random() * 0xFFFFFF).toString(16);
context.fillRect(Math.floor(Math.random() * canvas.width),
Math.floor(Math.random() * canvas.height),
Math.floor(Math.random() * canvas.width),
Math.floor(Math.random() * canvas.height));
}
let result;