tc.js

let celsius = document.getElementById('celsius');
    let fahrenheit = document.getElementById('fahrenheit');
    let kelvin = document.getElementById('kelvin');
    celsius.oninput = function () {
        let f = (parseFloat(celsius.value) * 9) / 5 + 32;
        fahrenheit.value = parseFloat(f.toFixed(2));
      
        let k = (parseFloat(celsius.value) + 273.15);
        kelvin.value = parseFloat(k.toFixed(2));
    }
    fahrenheit.oninput = function () {
        let c = ((parseFloat(
            fahrenheit.value) - 32) * 5) / 9;
        celsius.value = parseFloat(c.toFixed(2));
      
        let k = (parseFloat(
            fahrenheit.value) - 32) * 5 / 9 + 273.15;
        kelvin.value = parseFloat(k.toFixed(2));
    }
    kelvin.oninput = function () {
        let f = (parseFloat(
            kelvin.value) - 273.15) * 9 / 5 + 32;
        fahrenheit.value = parseFloat(f.toFixed(2));
      
        let c = (parseFloat(kelvin.value) - 273.15);
        celsius.value = parseFloat(c.toFixed(2));
    }