JSFiddle - React, Tailwind, and code Playground

HTML

<canvas width="400" height="400" id="cv"></canvas>

JavaScript

var cv  = $('#cv').get(0),
    ctx = cv.getContext('2d');

ctx.moveTo(0,0);
ctx.lineTo(10,10);
ctx.stroke();

var decoded = atob(cv.toDataURL().substr(22));

alert(decoded.substr(0, 20)); // part of png file
alert(decoded.length);        // length of png file