CanvasRenderingContext2D.bezierCurveTo()

html

<canvas id="canvas"></canvas>

js

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

ctx.beginPath();
ctx.moveTo(50, 20);
ctx.bezierCurveTo(230, 30, 150, 60, 50, 100);
ctx.stroke();

ctx.fillStyle = "blue";
// start point
ctx.fillRect(50, 20, 10, 10);
// end point
ctx.fillRect(50, 100, 10, 10);

ctx.fillStyle = "red";
// control point one
ctx.fillRect(230, 30, 10, 10);
// control point two
ctx.fillRect(150, 70, 10, 10);

<canvas id="canvas" width="400" height="200" class="playable-canvas"></canvas>
<div class="playable-buttons">
  <input id="edit" type="button" value="Edit" />
  <input id="reset" type="button" value="Reset" />
</div>
<textarea id="code" class="playable-code">
ctx.beginPath();
ctx.bezierCurveTo(50, 100, 180, 10, 20, 10);
ctx.stroke();</textarea
>

var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var textarea = document.getElementById("code");
var reset = document.getElementById("reset");
var edit = document.getElementById("edit");
var code = textarea.value;

function drawCanvas() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  eval(textarea.value);
}

reset.addEventListener("click", function () {
  textarea.value = code;
  drawCanvas();
});

edit.addEventListener("click", function () {
  textarea.focus();
});

textarea.addEventListener("input", drawCanvas);
window.addEventListener("load", drawCanvas);