Value change of range slider when drop-down tab changed

Question

I am trying to figure out how to change the value of a range slider when a drop-down unit menu is changed. For example, the slider is currently set to min -29, max 43, and step size 18 for "metric" drop-down. Thus, the range slider value is: -29, -11, 7, 25, 43. When the drop-down is changed to "imperial", I would like the range slider value to change to: -20, 12, 45, 77, 110. How can I program this in JavaScript? I would like to avoid using jQuery, since I have not been able to figure that out yet. Thank you in advance for your help.

<table style="margin-left: auto; margin-right: auto;width:75%;">
 <tr>
  <td style="text-align:right;width:40%;">
   <label for="unittype"><b>Units:</b></label>
  </td>
  <td style= "text-align:left;">
   <select id="unitselected" style="width:40%;" onChange="getunitType()">
    <option value="metric">Metric</option>
    <option value="imperial">Imperial</option>
   </select>
  </td>
</tr>
</table>

<label  id="tempunitresult" for"temp"><b>Temperature (&#8451;):</b></label>
 <br>
<input type="range" id="tempselected" class="slider" min="-29" step="18" max="43" oninput="rangeValueTemp.innerText=this.value">
<div style="text-align:center;" id="rangeValueTemp">7</div>

<script>
var unit_type = new Array();
  unit_type["metric"]=0;
  unit_type["imperial"]=1;

function getunitType(){
  var unitType = 0;
  var unitSelected = document.getElementById('unitselected');

  unitType = unit_type[unitSelected.value];

  if (unitType == 0){

    var tempValue = document.getElementById("tempselected");
    tempValue.setAttribute('min',-29);
    tempValue.setAttribute('max',43);
    tempValue.setAttribute('step',18);

  }else{

    var tempValue = document.getElementById("tempselected");
    tempValue.setAttribute('min',-20);
    tempValue.setAttribute('max',110);
}

</script>

Answer 1

Not sure ... but actually when changing units from metric (Celsius) to imperial (Fahrenheit) the range should stay the same.

So min/max
-29/43 °Celsius
should have an exact (convertible) equivalent of:
-20.2/109.4 °Fahrenheit

Otherwise you'll encountering conversion issues when switching units.

Example

let unitSelected = document.getElementById('unitselected');
let tempValue = document.getElementById("tempselected");
let rangeValueTemp = document.getElementById("rangeValueTemp");
let tempUnitString = document.getElementById("tempUnitString");
let tempUnitStringCurrent = document.getElementById("tempUnitStringCurrent");

// metric values
let minCelsius = -29;
let maxCelsius = 43;
let stepsCelsius = 18;
let initialValue = 7;

// imperial values
let minFahrenheit = minCelsius * 9 / 5 + 32;
let maxFahrenheit = maxCelsius * 9 / 5 + 32;
let stepsFahrenheit = 32.4;

//default values
let unitString = '°Celsius';
tempUnitString.textContent = unitString;
tempUnitStringCurrent.textContent = unitString;
tempselected.setAttribute('min', minCelsius);
tempselected.setAttribute('max', maxCelsius);
tempselected.setAttribute('step', stepsCelsius);
tempselected.value = initialValue;
let unitType = +unitselected.value;
let currentTemp = +tempselected.value;
rangeValueTemp.textContent = currentTemp;


//update temperature values
tempValue.addEventListener('change', function(e) {
  currentTemp = +e.currentTarget.value;
  rangeValueTemp.textContent = currentTemp;
})

//update temperature units 
unitSelected.addEventListener('change', function(e) {
  currentTemp = +tempselected.value;
  unitType = e.currentTarget.value;
  if (unitType == 'imperial') {
    unitString = '°Fahrenheit';
    currentTemp = currentTemp * 9 / 5 + 32;
    tempValue.setAttribute('step', stepsFahrenheit);
    tempValue.setAttribute('min', minFahrenheit);
    tempValue.setAttribute('max', maxFahrenheit);
  } else {
    unitString = '°Celsius';
    currentTemp = (currentTemp - 32) * 5 / 9;
    tempValue.setAttribute('min', minCelsius);
    tempValue.setAttribute('max', maxCelsius);
    tempValue.setAttribute('step', stepsCelsius);
  }
  currentTemp = +currentTemp.toFixed(3);
  rangeValueTemp.textContent = currentTemp;
  tempUnitString.textContent = unitString;
  tempUnitStringCurrent.textContent = unitString;
  tempselected.value = currentTemp;
});

input,
select {
  display: block;
  width: 100%;
}

label {
  font-weight: bold;
  display: block;
}

<p>
  <label id="tempunitresult" for "temp">
        Temperature (<span id="tempUnitString"></span>):
    </label>
  <input type="range" id="tempselected" class="slider">
</p>
<p>
  <label for="unittype">Units:</label>
  <select id="unitselected">
    <option value="metric">Metric (Celsius)</option>
    <option value="imperial">Imperial (Fahrenheit)</option>
  </select>
</p>
<p><span id="rangeValueTemp">0</span>&thinsp;<span id="tempUnitStringCurrent"></span></p>