Guy's what is wrong on my Programming?

Question

friends the answer is coming right but it is not staying it just blink out disappears.
have a look in it .and try to find out the error .

https://code.sololearn.com/Wo4YUoeTe2os/?ref=app

Answer 1

The reason is that default 'type' attribute of <button> element is 'submit'...
Instead of @Blue solution, better practice is to add explicit 'type="button"' to buttons that doesn't need to submit form:

<button onclick="myCal()" type="button">Press</button>

Answer 2

Ancient error! :D
in line 14, write
<form onsubmit='return false;'>

Answer 3

thanks a lot guys, it's work amazing .
actually I am not familiar with JavaScript so i am facing this type of common difficulties, by the way thanks again.