这应该是工作：

$(document).ready(function(){
    $('.button.next').click(function() {
       var target;
       $("p").each(function(i, element) {
         target = $(element).offset().top;
         if (target - 10 > $(document).scrollTop()) {
           return false; // break
         }
       });
       $("html, body").animate({
         scrollTop: target
       }, 700);
    });
    
    $('.button.prev').click(function() {
       var target;
       $("p").each(function(i, element) {
         current = $(element).offset().top;
         if (current + 10 > $(document).scrollTop()) {
           if (i == 0){
             target = 0;
           }
           else {
             target = $("p").eq(i-1).offset().top
           }
           return false; // break
         }
       });
       $("html, body").animate({
         scrollTop: target
       }, 700);
    });
});

p {
  height:600px;
}
.button {
  position:fixed;
  cursor:pointer;
  top:5%; 
} 
.next {
  right:5%;
}
.prev {
  right:15%;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class="button prev">PREV</div>
<div class="button next">NEXT</div>

<h1>Welcome to My Homepage</h1>

<p>This is the first paragraph.</p>
<p>This is the second paragraph.</p>
<p>This is the third paragraph.</p>
<p>This is the last paragraph.</p>