Smooth scrolling behavior improvement

[LaneSun]

I made some changes with your code, which makes the behavior in smooth scrolling mode more accurate (no more sluggishness when scrolling fast).

I hope you can adopt it

  scrollWithAnimation(event) {
// --     this.positionY = this.target.scrollTop;
    const acceleration = event.altKey ? Math.pow(this.settings.speed * this.settings.altMultiplier, 1.1) : Math.pow(this.settings.speed, 1.1);
    this.positionY += event.deltaY * acceleration;
    this.scrollDistance = event.deltaY * acceleration;
// ++
    this.positionY = Math.max(0, Math.min(this.positionY, this.target.scrollHeight - this.target.clientHeight));
// ++
    if (!this.isMoving) {
      this.isMoving = true;
      this.updateScrollAnimation();
    }
  }

[LaneSun]

There were some bugs when working with Typewriter Scroll, fixed.

  scrollWithAnimation(event) {
// <++
    if (!this.isMoving) {
        this.positionY = this.target.scrollTop;
    }
// ++>
// --     this.positionY = this.target.scrollTop;
    const acceleration = event.altKey ? Math.pow(this.settings.speed * this.settings.altMultiplier, 1.1) : Math.pow(this.settings.speed, 1.1);
    this.positionY += event.deltaY * acceleration;
    this.scrollDistance = event.deltaY * acceleration;
// <++
    this.positionY = Math.max(0, Math.min(this.positionY, this.target.scrollHeight - this.target.clientHeight));
// ++>
    if (!this.isMoving) {
      this.isMoving = true;
      this.updateScrollAnimation();
    }
  }
  updateScrollAnimation() {
    if (!this.isMoving || !this.target) {
// --       this.stopScrollAnimation();
// <++
      return this.stopScrollAnimation();
// ++>
    }
    const divider = Math.pow(this.animationSmoothness, 1.3);
    const delta = this.positionY - this.target.scrollTop;
    this.target.scrollTop += delta / divider;
    if (delta < 0 && this.positionY < 0 && this.target.scrollTop === 0) {
      return this.stopScrollAnimation();
    }
    if (delta > 0 && this.positionY > this.target.scrollHeight - this.target.clientHeight / 2 - this.scrollDistance) {
      return this.stopScrollAnimation();
    }
// --     if (Math.abs(delta) < this.scrollDistance * 0.015 || Math.abs(delta) < 1) {
// <++
    if (Math.abs(delta) < this.scrollDistance * 0.015 || Math.abs(delta / divider) < 1) {
// ++>
      return this.stopScrollAnimation();
    }
    window.requestAnimationFrame(this.updateScrollAnimation.bind(this));
  }
  stopScrollAnimation() {
    this.isMoving = false;
    this.scrollDistance = 0;
// <++
    this.positionY = this.target.scrollTop;
// ++>
    if (this.target)
      this.target = void 0;
  }

[flolu]

@LaneSun I really appreciate your contributions! Can you please create a pull request? If everything works fine, I will add your changes

[LaneSun]

It's done 😄

[flolu]

Thank you so much! Merged with #5