Input value jqeury check length and value checking

I'm still stuck here when validating the value of the input. If the value is between 0.4 and 0.9 the input n2 will remove the read-only. On another hand where if value less than 0.4 or more than 0.9 it will show up modal dialog. My question here is to validate the value/length if the value key in by the user is not in decimal value? let say user insert value 1, then my jquery won't firing out because my length is >=3.. if I put the length check > 1, then when user key the decimal value for example 0.5, the modal dialog will pop out 3 times.. since my length value is >= 3.. if I remove the length checking, it will keep pop out the modal dialog whenever user key in value length that more than one. My question is how to control such a situation if the valid range value is between 0.4 to 0.9, at the same time can checking value that not in decimal number as well? Is it possible?

<input type="text" class="form-control input-sm da" name="da" id="da" value="" autocomplete="off" />

<div class="form-group actionDiv" style="display:none">
<label for="cdaaction">Action </label>
<input type="text" class="form-control input-sm cdaaction" name="cdaaction" id="cdaaction" value="" />
</div>

<input type="text" class="form-control input-sm n2" name="n2" id="n2" value="" autocomplete="off" readonly />

$(document).ready(function() {
            $(".da").keyup(function() {
            var dInput = $(this).val();

            if ($('.da').val().length >= 3) 
            {
                if(dInput < 0.4 || dInput > 0.9)
                {
                    var mymodal = $('#mi-modal');
                    mymodal.find('.modal-body').html('Is the value correct: '+ $('.da').val() +'  ?');
                    mymodal.find('.modal-footer').html('<button type="button" class="btn btn-default" id="modal-btn-si">Yes</button><button type="button" class="btn btn-primary" id="modal-btn-no">No</button>');
                    $("#mi-modal").modal('show');

                    $("#modal-btn-si").on("click", function(){
                    $("#mi-modal").modal('hide');
                    $('.actionDiv').show();
                    });

                    $("#modal-btn-no").on("click", function(){
                    $("#mi-modal").modal('hide');
                    $('.actionDiv').hide();
                    $("#da").focus();
                    });
                    $(".n2").attr('readonly', true);

                }
                else
                {
                    $(".n2").removeAttr("readonly");
                    $('.actionDiv').hide();
                }
            }


            });
        });