how to calculate the fill color between dots in input type="range" when min val is not 0

I am struggling with the calculation that is responsible for the fill color between the 2 dots in the range price-slider.

Part of the html for the range slider is:

 <div class="values">
    <span id="range1">0</span>
    <span> &dash; </span>
    <span id="range2">100</span>
 </div>
 <div class="container">
    <div class="slider-track"></div>
    <input type="range" min="0" max="80" value="50" id="slider-1" oninput="slideOne()">
    <input type="range" min="0" max="80" value="70" id="slider-2" oninput="slideTwo()">
  </div>

The JS:

window.onload = function () {
  slideOne();
  slideTwo();
};

let sliderOne = document.getElementById("slider-1");
let sliderTwo = document.getElementById("slider-2");
let displayValOne = document.getElementById("range1");
let displayValTwo = document.getElementById("range2");
let minGap = 5;
let sliderTrack = document.querySelector(".slider-track");
let sliderMaxValue = document.getElementById("slider-1").max;

function slideOne() {
  if (parseInt(sliderTwo.value) - parseInt(sliderOne.value) <= minGap) {
    sliderOne.value = parseInt(sliderTwo.value) - minGap;
  }
  displayValOne.textContent = sliderOne.value;
  fillColor();
}
function slideTwo() {
  if (parseInt(sliderTwo.value) - parseInt(sliderOne.value) <= minGap) {
    sliderTwo.value = parseInt(sliderOne.value) + minGap;
  }
  displayValTwo.textContent = sliderTwo.value;
  fillColor();
}
function fillColor() {
   percent1 = (sliderOne.value / sliderMaxValue) * 100;
   percent2 = (sliderTwo.value / sliderMaxValue) * 100;
   sliderTrack.style.background = `linear-gradient(to right, #dadae5 ${percent1}% , #3264fe ${percent1}% , #3264fe ${percent2}%, #dadae5 ${percent2}%)`;
}

When the input values in the html have value "0" (min="0"), everything works fine with the fill-color in between the dots. But when is set both input to min="40" per example, the percent1 and percent2 variables in the JS need to be recalculated. Otherwise the fill-color between the dots in not correct anymore.

So: what is the correct calculation for percent1 and percent2 in the JS in case min="20" or min="40" in the HTML input?

Example 1 with min="0": Fiddle 1

Example 2 with min="40": Fiddle 2

Solution

Calculations, as already mentioned, should use a range of possible values (max - min) instead of just using the maximum (max - 0).

On top of that, both sliders must have the same minimum value. Otherwise, the overall appearance and behavior will be inconsistent.

window.onload = function() {
  slideOne();
  slideTwo();
};

const sliderOne = document.getElementById("slider-1");
const sliderTwo = document.getElementById("slider-2");
const displayValOne = document.getElementById("range1");
const displayValTwo = document.getElementById("range2");
const minGap = 5;
const sliderTrack = document.querySelector(".slider-track");
const sliderMaxValue = sliderOne.max;
const sliderMinValue = sliderOne.min;
const sliderValueRange = (sliderMaxValue - sliderMinValue);

function slideOne() {
  if (parseInt(sliderTwo.value) - parseInt(sliderOne.value) <= minGap) {
    sliderOne.value = parseInt(sliderTwo.value) - minGap;
  }
  displayValOne.textContent = sliderOne.value;
  fillColor();
}

function slideTwo() {
  if (parseInt(sliderTwo.value) - parseInt(sliderOne.value) <= minGap) {
    sliderTwo.value = parseInt(sliderOne.value) + minGap;
  }
  displayValTwo.textContent = sliderTwo.value;
  fillColor();
}

function fillColor() {
  const percent1 = (sliderOne.value - sliderMinValue) / sliderValueRange * 100;
  const percent2 = (sliderTwo.value - sliderMinValue) / sliderValueRange * 100;
  sliderTrack.style.background = `linear-gradient(to right, #dadae5 ${percent1}% , #3264fe ${percent1}% , #3264fe ${percent2}%, #dadae5 ${percent2}%)`;
}

.container {
  position: relative;
  width: 100%;
  height: 100px;
  margin-top: 30px;
}

input[type="range"] {
  -webkit-appearance: none;
  -moz-appearance: none;
  appearance: none;
  width: 100%;
  outline: none;
  position: absolute;
  margin: auto;
  top: 0;
  bottom: 0;
  background-color: transparent;
  pointer-events: none;
}

.slider-track {
  width: 100%;
  height: 5px;
  position: absolute;
  margin: auto;
  top: 0;
  bottom: 0;
  border-radius: 5px;
}

input[type="range"]::-webkit-slider-runnable-track {
  -webkit-appearance: none;
  height: 5px;
}

input[type="range"]::-moz-range-track {
  -moz-appearance: none;
  height: 5px;
}

input[type="range"]::-ms-track {
  appearance: none;
  height: 5px;
}

input[type="range"]::-webkit-slider-thumb {
  -webkit-appearance: none;
  height: 1.7em;
  width: 1.7em;
  background-color: #3264fe;
  cursor: pointer;
  margin-top: -9px;
  pointer-events: auto;
  border-radius: 50%;
}

input[type="range"]::-moz-range-thumb {
  -webkit-appearance: none;
  height: 1.7em;
  width: 1.7em;
  cursor: pointer;
  border-radius: 50%;
  background-color: #3264fe;
  pointer-events: auto;
  border: none;
}

input[type="range"]::-ms-thumb {
  appearance: none;
  height: 1.7em;
  width: 1.7em;
  cursor: pointer;
  border-radius: 50%;
  background-color: #3264fe;
  pointer-events: auto;
}

input[type="range"]:active::-webkit-slider-thumb {
  background-color: #ffffff;
  border: 1px solid #3264fe;
}

.values {
  background-color: #3264fe;
  width: 32%;
  position: relative;
  margin: auto;
  padding: 10px 0;
  border-radius: 5px;
  text-align: center;
  font-weight: 500;
  font-size: 25px;
  color: #ffffff;
}

.values:before {
  content: "";
  position: absolute;
  height: 0;
  width: 0;
  border-top: 15px solid #3264fe;
  border-left: 15px solid transparent;
  border-right: 15px solid transparent;
  margin: auto;
  bottom: -14px;
  left: 0;
  right: 0;
}

<div class="values">
  <span id="range1">0</span>
  <span> &dash; </span>
  <span id="range2">100</span>
</div>
<div class="container">
  <div class="slider-track"></div>
  <input type="range" min="40" max="80" value="50" id="slider-1" oninput="slideOne()">
  <input type="range" min="40" max="80" value="70" id="slider-2" oninput="slideTwo()">
</div>