form submit

const XHR = new XMLHttpRequest(),
	FD = new FormData();
	FD.append("EMAIL", "nekmail@gmail.com");	  
	XHR.open( 'post', 'https://subscriptionurl' );
  	XHR.send( FD );

<form action="https://subscriptionurl" method="post" id="mc-embedded-subscribe-form" name="mc-embedded-subscribe-form" class="validate" target="_blank" novalidate>    

<div class="mc-field-group">
              <label for="mce-EMAIL">Email Address </label>
              <input type="email" value="" name="EMAIL" class="required email" id="mce-EMAIL">
</div>
    <div class="clear"><input type="submit" value="Subscribe" name="subscribe" id="mc-embedded-subscribe" class="button"></div> 
</form>