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">
									</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

$.fn.extend({
	has_value: function() {
		return this.filter( function() {
			return $( this ).val().length == 0;
		}).length;
	}
});

var $input = $( 'input.form-control' ),
	$register = $('#signin');

$input.on( 'change keyup', function() {
	$register.prop( 'disabled', $input.has_value() ); 		
});	

$input.trigger( 'change' );