How do I add transition to the effect of hide() and show() on these elements?

Question

In the following SSCCE, how can I animate the appearance of .items using show() and their disappearance using hide(), such that it looks like the item5, item6, item7, item8 have flown into the viewport?

That is, what I want is that when the .next-arrow is clicked, for example for the first time, the hiding of item1, item2, item3, item4, and the showing of item5, item6, item7, item8, is "transitioned" - just like new pages flow into the viewport in this website.

How can I do that?

$(document).ready(function() {
  //alert('ready');//check

  var numberOfItems = $('.item').length;
  //alert('numberOfItems => ' + numberOfItems);//check

  displayNextArrowOnCondition();
  displayPreviousArrowOnCondition();



  /**
   *
   **/
  $('a.next-arrow').click(function(event) {
    event.preventDefault();

    var currentFirstItem = getCurrentFirstItem(); // Difference between var and no var SO: If you're in the global scope then there's no difference. If you're in a function then var will create a local variable, "no var" will look up the scope chain until it finds the variable or hits the global scope (at which point it will create it):

    $('div.item' + currentFirstItem).hide(); //We don't need to have the condition of checking this element's existence because the next-arrow whose handler this method is, appears only if the numberOfItems is greater than the id of the item with the greatest id among the elements currently visible on the screen.
    if (('div.item' + (currentFirstItem + 1)).length) { //SO: How can I check the existence of an element in jQuery?? In JavaScript, everything is truthy or falsy and for numbers, 0 means false, everything else true. So you could write: "if ($(selector).length)" - and you don't need that > 0 part.
      $('div.item' + (currentFirstItem + 1)).hide();
    }
    if (('div.item' + (currentFirstItem + 2)).length) {
      $('div.item' + (currentFirstItem + 2)).hide();
    }
    if (('div.item' + (currentFirstItem + 3)).length) {
      $('div.item' + (currentFirstItem + 3)).hide();
    }

    hidePreviousArrow();
    hideNextArrow();

    displayPreviousArrowOnCondition();
    displayNextArrowOnCondition();
  });


  /**
   *
   **/
  $('a.previous-arrow').click(function(event) {
    event.preventDefault();

    var currentFirstItem = getCurrentFirstItem();

    $('div.item' + (currentFirstItem - 1)).show();

    if (('div.item' + (currentFirstItem - 2)).length) {
      $('div.item' + (currentFirstItem - 2)).show();
    }
    if (('div.item' + (currentFirstItem - 3)).length) {
      $('div.item' + (currentFirstItem - 3)).show();
    }
    if (('div.item' + (currentFirstItem - 4)).length) {
      $('div.item' + (currentFirstItem - 4)).show();
    }

    hidePreviousArrow();
    hideNextArrow();

    displayPreviousArrowOnCondition();
    displayNextArrowOnCondition();
  });



  /**
   * DISPLAY NEXT ARROW WHEN
   * 1. NUMBER OF ITEMS IS GREATER THAN THE id OF THE LAST ITEM DISPLAYED IN THE CURRENT VIEWPORT
   **/
  function displayNextArrowOnCondition() {
    //alert('displayNextArrowOnCondition called');//check
    //Iterate through items in OPPOSTIE order, and when found the first one which is not hidden by hide() or display:none, assign it to currentLastItem (because this is the first item in the viewport), and break out from the loop.
    var currentLastItem = getCurrentLastItem();
    //alert('currentLastItem -> ' + currentLastItem);//check
    if (currentLastItem < numberOfItems) {
      $('a.next-arrow').css('display', 'block');
      $('.wrapper').mouseover(function() {
        //$('a.next-arrow').css('visibility', 'visible');
      });
      $('.wrapper').mouseleave(function() {
        //$('a.next-arrow').css('visibility', 'hidden');
      });
    }
  }


  /**
   * DISPLAY PREVIOUS ARROW WHEN
   * 1. THE id OF THE FIRST DISPLAYED ITEM IS GREATER THAN 4
   **/
  function displayPreviousArrowOnCondition() {
    //Iterate through items in order, and when found the first one which is not hidden by hide() or display:none, assign it to currentFirstItem (because this is the first item in the viewport), and break out from the loop.
    var currentFirstItem = getCurrentFirstItem();
    if (currentFirstItem > 4) {
      $('a.previous-arrow').css('display', 'block');
      $('.wrapper').mouseover(function() {
        $('a.previous-arrow').css('visibility', 'visible');
      });
      $('.wrapper').mouseleave(function() {
        $('a.previous-arrow').css('visibility', 'hidden');
      });
    }
  }


  /**
   * DISPLAY:NONE NEXT ARROW IF IT IS VISIBLE
   **/
  function hideNextArrow() {
    //alert('hideNextArrow called');//check
    if ($('a.next-arrow').css('display').toLowerCase() == 'block') { //The == operator will compare for equality after doing any necessary type conversions. The === operator will not do the conversion, so if two values are not the same type === will simply return false.| Just in case anyone was wondering in 2012: === is way faster than ==. jsperf.com/comparison-of-comparisons.
      //alert('YES if ($(\'a.next-arrow\').attr(\'display\').toLowerCase() == \'block\'). SO I AM CHANGING IT TO none.');//check
      $('a.next-arrow').css('display', 'none');
    } //else { alert('NO  if ($(\'a.next-arrow\').attr(\'display\').toLowerCase() == \'block\').'); } //check
  }


  /**
   * DISPLAY:NONE PREVIOUS ARROW IF IT IS VISIBLE
   **/
  function hidePreviousArrow() {
    //alert('hidePreviousArrow called');//check
    //alert($('a.previous-arrow').css('display'));//check
    if ($('a.previous-arrow').css('display') == 'block') {
      //alert('YES if ($(\'a.previous-arrow\').attr(\'display\').toLowerCase() == \'block\'). SO I AM CHANGING IT TO none.');//check
      $('a.previous-arrow').css('display', 'none');
    } //else { alert('NO  if ($(\'a.previous-arrow\').attr(\'display\').toLowerCase() == \'block\').'); } //check
  }


  /**
   *
   **/
  function getCurrentFirstItem() {
    for (i = 1; i <= numberOfItems; i++) {
      if ($("#" + i).visible(true, true)) {
        //alert('YES if (  $("#"+i).visible(true, true)  )');//check
        currentFirstItem = i;
        break;
      } //else { //alert('NO if (  $("#"+i).visible(true, true)  )'); }//check 
    }
    //alert('currentFirstItem -> ' + currentFirstItem);//check
    return currentFirstItem;
  }


  /**
   *
   **/
  function getCurrentLastItem() {
    for (j = numberOfItems; j >= 1; j--) {
      if ($("#" + j).visible(true, true)) {
        //alert("YES if (  $(\"#\"+j).visible(true, true) ) ");//check
        currentLastItem = j;
        break;
      } //else { //alert('NO if (  $("#"+j).visible(true, true) )'); } //check
    }
    //alert('currentLastItem -> ' + currentLastItem);//check
    return currentLastItem;
  }

});

html,
body,
body div,
span,
object,
iframe,
h1,
h2,
h3,
h4,
h5,
h6,
p,
blockquote,
pre,
abbr,
address,
cite,
code,
del,
dfn,
em,
img,
ins,
kbd,
q,
samp,
small,
strong,
sub,
sup,
var,
b,
i,
dl,
dt,
dd,
ol,
ul,
li,
fieldset,
form,
label,
legend,
table,
caption,
tbody,
tfoot,
thead,
tr,
th,
td,
article,
aside,
figure,
footer,
header,
hgroup,
menu,
nav,
section,
time,
mark,
audio,
video,
details,
summary {
  margin: 0px;
  padding: 0px;
  border: 0px none;
  background: transparent none repeat scroll 0% 0%;
  font-size: 100%;
  vertical-align: baseline;
}
.wrapper {
  position: relative;
  white-space: nowrap;
  overflow: hidden;
}
div.item {
  /*position:absolute;*/
  display: inline-block;
  width: 25%;
  height: 25vw;
}
.item1 {
  left: 0%;
  background-color: wheat;
}
.item2 {
  left: 25%;
  background-color: pink;
}
.item3 {
  left: 50%;
  background-color: beige;
}
.item4 {
  left: 75%;
  background-color: gainsboro;
}
.item5 {
  left: 100%;
  background-color: coral;
}
.item6 {
  left: 125%;
  background-color: crimson;
}
.item7 {
  left: 150%;
  background-color: aquamarine;
}
.item8 {
  left: 175%;
  background-color: darkgoldenrod;
}
.item9 {
  left: 200%;
  background-color: khaki;
}
.item10 {
  left: 225%;
  background-color: indianred;
}
.item11 {
  left: 250%;
  background-color: mediumspringgreen;
}
.previous-arrow,
.next-arrow {
  width: 30px;
  height: 50%;
  top: 50%;
  position: absolute;
  opacity: 0.7;
  color: white;
  background-repeat: no-repeat;
  margin-top: -30px;
  display: none;
}
.previous-arrow {
  background-image: url(a2.png);
  left: 0px;
}
.next-arrow {
  background-image: url(b2.png);
  right: 0px;
}
.previous-arrow,
.next-arrow {
  opacity: 1;
}
body {
  background-color: black;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="http://cdn.jsdelivr.net/jquery.visible/1.1.0/jquery.visible.min.js"></script>

<div class="wrapper">
  <a class="previous-arrow" href="">&gt;</a>-->
  <!--
		-->
  <div id="1" class="item item1 wheat">a.</div>
  <!--
		-->
  <div id="2" class="item item2 pink">a.</div>
  <!--
		-->
  <div id="3" class="item item3 beige">a.</div>
  <!--
		-->
  <div id="4" class="item item4 gainsboro">a.</div>
  <!--
		-->
  <div id="5" class="item item5 coral">a.</div>
  <!--
		-->
  <div id="6" class="item item6 crimson">a.</div>
  <!--
		-->
  <div id="7" class="item item7 darkgoldenrod">a.</div>
  <!--
		-->
  <div id="8" class="item item8 aquamarine">a.</div>
  <!--
		-->
  <div id="9" class="item item9 aquamarine">a.</div>
  <!--
		-->
  <div id="10" class="item item10 aquamarine">a.</div>
  <!--
		-->
  <div id="11" class="item item11 aquamarine">a.</div>
  <!--
		--><a class="next-arrow" href="">&lt;</a>	
</div>

Answer 1

If you want use show() and hide() only, you can use show('slow') and hide('slow'), etc. Other than that there are many ways and effects you can use.

Please follow this link to get to know how many ways were there to do this.

jQuery Effects

Answer 2

You can use css transitions or css animations. Animations like:

1. Define css class rules and assign class name to the elements you want to animate

.doFadeIn {
    -webkit-animation:fadeInSlide forwards ease-in 150ms;
    animation:fadeInSlide forwards ease-in 150ms;
}
.doFadeOut {
    -webkit-animation:fadeOutSlideDown forwards ease-out 150ms;
    animation:fadeOutSlideDown forwards ease-out 150ms;
}

2. Define keyframes for the animations

    @keyframes fadeInSlide
    {
         0% { opactity:0; transform: translateX(-100px); }
         100% { opactity:1; transform: translateX(0); }
    } 

When assigning doFadeIn to the class name of elements, they will: Fade in - opacity:0 to 1 (0% visible to 100% visible) Moves along the horizontal axis (X) 100px left of the elements original position to it's original position.

It will do this spanning the duration of 150 milli-seconds

<div id="my-widget1" class="my-widget"><div>
  
<div id="my-widget1" class="my-widget doFadeIn"><div>