усовершенствовать js код

window.addEventListener("scroll", function() { 
	let Y = this.pageYOffset+this.innerHeight, 
		h = document.querySelector('header'), 
		tH = document.querySelector('.topHeader'), 
		sH = document.querySelector('.subHeader'); 
	[[1000,h,"minWidth"],[2000,tH,"mTop"],[3000,tH,"maxHeight"],[4000,sH,"dblock"]] 
	.filter((a)=>a[1].classList[Y > a[0] ? "add" : "remove"](a[2])); 
});

html { height: 4100px } 
 
body *::before { position: fixed; content: attr(class) } 
 
.topHeader::before { margin-top: 20px } 
 
.subHeader::before { margin-top: 40px }

<header></header> 
<div class="topHeader"></div> 
<div class="subHeader"></div>

window.onscroll = function () {
  var scrolled = window.pageYOffset,
    header = qS('header'),
    topHeader = qS('.topHeader'),
    subHeader = qS('.subHeader'),
    a = scrolled > 1000,
    b = scrolled > 2000,
    c = scrolled > 3000,
    d = scrolled > 4000;
  if (!!a) {
    header.classList.add('minWidth');
    header.style.top = scrolled + 'px';
  } else {
    header.classList.remove('minWidth');
    header.style.top = '0';
  }

  function qS(el) {
    return document.querySelector(el);
  }

  function checkPos(condition, elem, className) {
    if (!!condition) {
      return elem.classList.add(className)
    } else {
      return elem.classList.remove(className)
    }
  }
  checkPos(b, topHeader, 'mTop');
  checkPos(c, topHeader, 'maxHeight');
  checkPos(d, subHeader, 'dblock');
}

А может как то так? На работоспособность не проверял :(

window.onscroll = function () {
var scrolled = window.pageYOffset,
header = document.querySelector('header'),
topHeader = document.querySelector('.topHeader'),
subHeader = document.querySelector('.subHeader');
function move(headerType, addOrRemove, styleClass){
    headerType.classList.addOrRemove(styleClass);
}
switch(scrolled){
  case scrolled > 1000: move(header, add, minWidth);
                        header.style.top = scrolled + 'px';
                        break;
  case scrolled > 2000: move(topHeader, add, mTop);
                        break;
  case scrolled > 3000: move(topHeader, add, maxHeight);
                        break;
  case scrolled > 4000: move(topHeader, add, dblock);
                        break;  
  default: move(header, remove, minWidth);
           header.style.top = '0';
           move(header, remove, mTop);
           move(header, remove, maxHeight);
           move(header, remove, dblock);
           break;                                                              
}
}