Write value of range to thumb slider

I want to write the value of range input to the thumb. I looked to every single question about this I could find on Google and I didn't find a solution. I also want to when the value is 10001 I want it to show ∞ instead.

I have tried:

$('#km').on('input', function() {
  if ($(this).val() === "10001") {
    console.log("infinity");
    $(this).addClass("range-infinite")
  } else {
    $(this).removeClass("range-infinite");
  }
});

.range {
  -webkit-appearance: none;
  -moz-apperance: none;
  background-image: linear-gradient(to right, #1299E6, #A0D9F9);
  width: 90%;
  margin-left: 70px;
  height: 1px;
  margin-bottom: 40px;
  border-top: none;
}

.range::-webkit-slider-thumb {
  appearance: none;
  -webkit-appearance: none;
  -moz-apperance: none;
  height: 30px;
  width: 80px;
  background: #1299E6;
  border: 1px solid #A0D9F9;
  border-radius: 40px;
}

.range::-webkit-slider-thumb::before {
  content: attr(data-val)
}

.range-infinite::before {
  content: "∞";
}

.range input[type=range] {
  border: none;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class="range-div">
  <input type="range" name="" id="" class="range">
</div>

but it doesn't seem to work.
Any help is appreciated.

Solution

:before and :after pseudo will not work on Form Action elements like input.
Instead use a span for example.

const els = (sel, par = document) => par.querySelectorAll(sel);

els(".range").forEach((elRange) => {
  elRange.addEventListener("input", () => {
    let val = elRange.valueAsNumber;
    val = val >= parseInt(elRange.max, 10) ? "∞" : val;
    elRange.nextElementSibling.dataset.val = val;
  });
  elRange.dispatchEvent(new Event("input"));
});

.range ~ output::before {
  content: attr(data-val);
  margin-right: 0.2em;
}

<input type="range" name="" class="range" min=0 max=10001 step=1 value=0>
<output>km</output>

Create a custom range input

If you want the <output> element to follow-up with your value you could:

Position your output absolute in a relative parent.
Calculate and transform your value into thumb position px or %.
Here's an example that uses CSS variables:

const els = (sel, par = document) => par.querySelectorAll(sel);
const el = (sel, par = document) => par.querySelector(sel);

els(".range").forEach((elRange) => {
  const elInput = el("input", elRange);
  const elOutput = el("output", elRange);
  const thumbWidth = 100; // Same as in CSS

  const max = parseInt(elInput.max, 10);

  const calc = () => {
    const val = elInput.valueAsNumber;
    const txt = val >= max ? "∞" : val;
    const xPX = val * (elInput.offsetWidth - thumbWidth) / max; // px
    const xPC = xPX * 100 / elInput.offsetWidth; // %
    elOutput.style.setProperty("--x", xPC);
    elOutput.dataset.val = txt;
  };

  elInput.addEventListener("input", calc);
  addEventListener("resize", calc);
  elInput.dispatchEvent(new Event("input"));
});

/* QuickReset */
* {
  margin: 0;
  box-sizing: border-box;
}

html,
body {
  min-height: 100%;
  font: 1rem/1.4 system-ui, sans-serif;
}


/* CUSTOM RANGE INPUT */

.range {
  --thumbWidth: 100;
  --thumbHeight: 30;
  --sliderHeight: 10;

  position: relative;
  display: flex;
  height: calc(var(--thumbHeight) * 1px);
  touch-action: none;
  color: #fff;
  margin: 2em;

  input {
    appearance: none;
    -webkit-appearance: none;
    -moz-appearance: none;
    background-image: linear-gradient(to right, #1299E6, #A0D9F9);
    width: 100%;
    height: calc(var(--sliderHeight) * 1px);
    margin: auto 0;
    outline: none;

  }

  input:active::-webkit-slider-thumb {
    box-shadow: 0 2px 5px -2px rgba(0, 0, 0, 0.4);
  }

  input::-webkit-slider-thumb {
    appearance: none;
    -webkit-appearance: none;
    -moz-appearance: none;
    height: calc(var(--thumbHeight) * 1px);
    width: calc(var(--thumbWidth) * 1px);
    background: #1299E6;
    border-radius: 30px;
    cursor: grab;
    box-shadow: 0 0 0 0.2em #fff;
  }

  output {
    --x: 0;
    position: absolute;
    display: flex;
    align-items: center;
    justify-content: center;
    left: calc(var(--x) * 1%);
    width: calc(var(--thumbWidth) * 1px);
    height: 100%;

    font-size: 0.85em;
    pointer-events: none;

    &::before {
      content: attr(data-val);
      margin-right: 0.5em;
    }
  }
}

<div class="range">
  <input type="range" name="km" min=0 max=10001 step=1 value=0>
  <output>km</output>
</div>