JSFiddle - React, Tailwind, and code Playground

HTML

<div class="form-group">
									<label for="txtusername" class="col-sm-4 control-label">Username</label>
									<div class="col-sm-8">
										<input type="text" class="form-control" id="txtusername" value="asd" name="txtusername" placeholder="Username">
									</div>
								</div>
								<div class="form-group">
									<label for="txtpassword" class="col-sm-4 control-label">Password</label>
									<div class="col-sm-8">
										<input  type="password" class="form-control" value="" id="txtpassword" name="txtpassword" placeholder="Password">
									</div>
								</div>
								<div class="form-group">
									<div class="col-sm-offset-4 col-sm-8">
										<div class="checkbox">
											<label><input type="checkbox">Remember me</label>
										</div>
									</div>
								</div>
								<div class="form-group">
									<div class="col-sm-offset-4 col-sm-8">
										<button type="submit" id="signin" class="btn btn-default"  >Sign in</button>

									</div>

JavaScript

var $input = $('input'),
            $register = $('#signin');
            $register.attr('disabled', true);

var checkInput = function(){
    var trigger = false;
                $input.each(function() {
                    if (!$(this).val()) {
                        trigger = true;
                    }
                });
                trigger ? $register.attr('disabled', true) : $register.removeAttr('disabled');
}

$input.keyup( function(){
    checkInput();
} );
    
$(document).ready( function(){
    checkInput(); 
    } );