CanvasRenderingContext2D.miterLimit

<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.moveTo(0,0);
ctx.lineWidth = 15;
ctx.lineTo(100, 100);
ctx.stroke();
</textarea>

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

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

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

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

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