Basic Canvas Drawing

gistfile1.js

// add some interactivity

var canvas = document.querySelector("#canvas"),
    ctx = canvas.getContext("2d");



ctx.beginPath();

ctx.lineWidth = 10;
ctx.strokeStyle = 'lime';
ctx.lineCap = 'round';
ctx.lineJoin = 'round';

ctx.moveTo(10,10);
ctx.lineTo(10,100);
ctx.lineTo(100, 100);
ctx.lineTo(100, 10);
ctx.lineTo(10, 10);

ctx.stroke();

function onMouseMove(e)
{
  var mouseX = e.clientX;
  var mouseY = e.clientY;

  ctx.lineTo(mouseX, mouseY);
  ctx.stroke();
}

canvas.addEventListener("mousemove", onMouseMove, false);