Changing color based on gauge value – Javascript

May 22, 2023

I’m trying to write a Javascript function to go alongside a gauge that I copied online, the gauge works like this:

const gaugeElement = document.querySelector(".gauge");

function setGaugeValue(gauge, value) {
  if (value < 0 || value > 1) {
    return;
  }

  gauge.querySelector(".gauge__fill").style.transform = `rotate(${value / 2}turn)`;
  gauge.querySelector(".gauge__cover").textContent = `${Math.round(value * 100)}%`;

}

setGaugeValue(gaugeElement, 0.26);

<div class="card">
  <div class="FuelLevelText">
    <h3>Fuel Level</h3>
  </div>
  <div class="gauge">
    <div class="gauge__body">
      <div id="gaugecolor" class="gauge__fill"></div>
      <div class="gauge__cover"></div>
    </div>
  </div>
</div>

There’s also a bit of CSS that goes with this

This works fine to change the gaugeElement value and will change the percentage on screen, however I’d like to add a rule so if the value goes below 0.05 or 5% the gauge fill background-color turns red to indicate it’s running low. I’m very very new to coding so I’m struggling to find a resource online that has something similar to what I need that I can adapt to my needs.

I tried adding a line:

if (gaugeElement, '< 0.05') {
    function changebackground(color) {
        #gaugecolor = color;
    }

    changebackground('red');
}

However I don’t know enough Javascript to know if this is even targeting the right section?

>Solution :

If the value goes below 0.05 or 5% the gauge fill background-color turns red.


const gaugeElement = document.querySelector(".gauge");

function setGaugeValue(gauge, value) {
  if (value < 0 || value > 1) {
    return;
  }

  gauge.querySelector(".gauge__fill").style.transform = `rotate(${value / 2}turn)`;
  gauge.querySelector(".gauge__cover").textContent = `${Math.round(value * 100)}%`;

  if (value < 0.05) {
    gauge.querySelector(".gauge__fill").style.backgroundColor = 'red';
  } else {
    gauge.querySelector(".gauge__fill").style.backgroundColor = ''; // Reset the background color
  }
}

setGaugeValue(gaugeElement, 0.26);