how to format input box text as I am typing it

Pure JS (Sans jQuery):

var fnf = document.getElementById("formattedNumberField");
fnf.addEventListener('keyup', function(evt){
    var n = parseInt(this.value.replace(/\D/g,''),10);
    fnf.value = n.toLocaleString();
}, false);

Native JS Example Fiddle

With jQuery:

$("#formattedNumberField").on('keyup', function(){
    var n = parseInt($(this).val().replace(/\D/g,''),10);
    $(this).val(n.toLocaleString());
    //do something else as per updated question
    myFunc(); //call another function too
});

With jQuery Example Fiddle

To allow decimals:

$("#formattedNumberField").on('keyup', function(evt){
    if (evt.which != 110 ){//not a fullstop
        var n = parseFloat($(this).val().replace(/\,/g,''),10);
        $(this).val(n.toLocaleString());
    }
});

Obligatory Example