试试这个

$('#from-amount').keypress(function(event) {
    if (((event.which != 46 || (event.which == 46 && $(this).val() == '')) ||
            $(this).val().indexOf('.') != -1) && (event.which < 48 || event.which > 57)) {
        event.preventDefault();
    }
}).on('paste', function(event) {
    event.preventDefault();
});

https://jsfiddle.net/4rsv960t/1/