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" 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" id="txtpassword" name="txtpassword" placeholder="Password" value = '123456'>
									</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:not(:checkbox)'),// Check box is having some value even when not checked so ommitting it.
            $register = $('#signin');
            $register.attr('disabled', isBlankForm());

function isBlankForm(){
    var isBlank = true;
    $input.each(function(){
        if(!!$(this).val()) isBlank = false;
    })
    return isBlank
}

$input.keyup(function() {
    $register.prop('disabled', isBlankForm())
});