Turtle code in JS

turtle.js

class Turtle {
  constructor(ox, oy, ctx) {
    this.ctx = ctx;
    this.ox = ox;
    this.oy = oy;
    this.reset();
  }

  reset() {
    this.x = this.ox;
    this.y = this.oy;
    this.angle = 0;
    this.pen = true;
  }

  radians(n) {
    return (Math.PI * n) / 180.0;
  }

  fwd(n) {
    const nx = this.x + n * Math.cos(this.radians(this.angle - 90));
    const ny = this.y + n * Math.sin(this.radians(this.angle - 90));
    if (this.pen) {
      this.ctx.moveTo(this.x, this.y);
      this.ctx.lineTo(nx, ny);
      this.ctx.stroke();
    }
    this.x = nx;
    this.y = ny;
    return this;
  }

  back(n) {
    const curr = this.angle;
    this.angle += 180;
    this.fwd(n);
    this.angle = curr;
  }

  left(n) {
    this.angle -= n;
    return this;
  }

  right(n) {
    this.angle += n;
    return this;
  }

  penup() {
    this.pen = false;
    return this;
  }

  pendown() {
    this.pen = true;
    return this;
  }
}