HTML5 required attribute seems not working
Try putting it inside a form tag and closing the input tag:
<form>
<input type = "text" class = "txtPost" placeholder = "Post a question?" required />
<button class = "btnPost btnBlue">Post</button>
</form>
Make sure that novalidate attribute is not set to your form tag
Absence of Submit field element in the form also causes this error. In the case of "button" field handled by JS to submit form lacks the necessity of Submit button hence Required doesn't Work