JSFiddle - React, Tailwind, and code Playground

HTML

<label for="from">From:</label>
<select id="from">
    <option value="INR">INR</option>
    <option value="USD" selected>USD</option>
    <option value="GBP">GBP</option>
</select> <br />

<label for="amount">Amount: </label>
<input id= "amount" value='1' />

<label for="to">To:</label>
<select id="to">
    <option value="INR" selected>INR</option>
    <option value="USD">USD</option>
    <option value="GBP">GBP</option>
</select>

<div id="conversion"></div>

JavaScript

var rates = {"INR": 62.3, "USD": 1, "GBP": 0.62};

changeConversion();

$('#to, #from, #amount').change(function(){
    changeConversion();
});

function changeConversion()
{
    var fromKey = $('#from').val();
    var from = rates[fromKey];

    var toKey = $('#to').val();
    var to = rates[toKey];

    var amt = parseFloat($('#amount').val());

    var ans = parseFloat(to / from  * amt).toFixed(2);

    $('#conversion').html(ans);

}