text.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <div class="box" style="width: 100px">
      <canvas
        id="myCanvas"
        width="200"
        height="100"
        style="border: 1px solid #000000"
      >
      </canvas>
    </div>
  </body>
  <script>
    var c = document.getElementById("myCanvas");
    console.log("c", c.offsetWidth);
    var ctx = c.getContext("2d");
    ctx.lineWidth = 1;
    for (let i = 0; i < 200; i = i + 4) {
      ctx.moveTo(i + 0.5, 0);
      ctx.lineTo(i + 0.5, 100);
      ctx.stroke();
    }
  </script>
</html>