index.js

let celciusInput = document.querySelector('#celcius > input')
let fahrenheitInput = document.querySelector('#fahrenheit> input')
let kelvinInput = document.querySelector('#kelvin > input')

let btn = document.querySelector('.button button')


function roundNumber(number) {
    return Math.round(number * 100) / 100
}


/* Celcius to Fahrenheit and Kelvin */
celciusInput.addEventListener('input', function () {
    let cTemp = parseFloat(celciusInput.value)
    let fTemp = (cTemp * (9 / 5)) + 32
    let kTemp = cTemp + 273.15

    fahrenheitInput.value = roundNumber(fTemp)
    kelvinInput.value = roundNumber(kTemp)
})


/* Fahrenheit to Celcius and Kelvin */
fahrenheitInput.addEventListener('input', function () {
    let fTemp = parseFloat(fahrenheitInput.value)
    let cTemp = (fTemp - 32) * (5 / 9)
    let kTemp = (fTemp - 32) * (5 / 9) + 273.15

    celciusInput.value = roundNumber(cTemp)
    kelvinInput.value = roundNumber(kTemp)
})

/* Kelvin to Celcius and Fahrenheit */
kelvinInput.addEventListener('input', function () {
    let kTemp = parseFloat(kelvinInput.value)
    let cTemp = kTemp - 273.15
    let fTemp = (kTemp - 273.15) * (9 / 5) + 32

    celciusInput.value = roundNumber(cTemp)
    fahrenheitInput.value = roundNumber(fTemp)
})


btn.addEventListener('click', () => {
    celciusInput.value = ""
    fahrenheitInput.value = ""
    kelvinInput.value = ""
})