Select element in jQuery

<style>
  .cube {
    height: 100px;
    width: 100px;
    display: inline-block;
  }

  .sel {
    border: solid 2px blue;
  }
</style>

<div id="cubes">
  <div class="cube" style="background: red;"></div>
  <div class="cube" style="background: yellow;"></div>
  <div class="cube" style="background: red;"></div>
  <div class="cube sel" style="background: green;"></div>
  <div class="cube" style="background: green;"></div>
  <div class="cube" style="background: red;"></div>
  <div class="cube" style="background: yellow;"></div>
</div>
<button onclick="next()">next</button>
<button onclick="nextAll()">nextAll</button>
<button onclick="prev()">prev</button>
<button onclick="prevAll()">prevAll</button>
<button onclick="first()">first</button>
<button onclick="last()">last</button>
<button onclick="parent()">parent</button>
<button onclick="childrenF()">children</button>
<button onclick="filterRed()">filter red</button>
<button onclick="filterGreen()">filter green</button>
<button onclick="filterYellow()">filter yellow</button>
<button onclick="notRed()">not red</button>
<button onclick="notGreen()">not green</button>
<button onclick="notYellow()">not yellow</button>

<script>
  function next() {
    $(".sel").removeClass("sel").next().addClass("sel");
  }

  function nextAll() {
    $(".sel").removeClass("sel").nextAll().addClass("sel");
  }

  function prev() {
    $(".sel").removeClass("sel").prev().addClass("sel");
  }

  function prevAll() {
    $(".sel").removeClass("sel").prevAll().addClass("sel");
  }

  function first() {
    $(".sel").removeClass("sel");
    $("#cubes").children().first().addClass("sel");
  }

  function last() {
    $(".sel").removeClass("sel");
    $("#cubes").children().last().addClass("sel");
  }

  function parent() {
    $(".sel").removeClass("sel").parent().addClass("sel");
  }

  function childrenF() {
    $(".sel").removeClass("sel").children().addClass("sel");
  }

  function filterRed() {
    $(".sel").removeClass("sel");
    $("#cubes").children().filter(function (index) {
      return this.style["background-color"] == "red";
    }).addClass("sel");
  }

  function filterGreen() {
    $(".sel").removeClass("sel");
    $("#cubes").children().filter(function (index) {
      return this.style["background-color"] == "green";
    }).addClass("sel");
  }

  function filterYellow() {
    $(".sel").removeClass("sel");
    $("#cubes").children().filter(function (index) {
      return this.style["background-color"] == "yellow";
    }).addClass("sel");
  }

  function notRed() {
    $(".sel").removeClass("sel");
    $("#cubes").children().not(function (index) {
      return this.style["background-color"] == "red";
    }).addClass("sel");
  }

  function notGreen() {
    $(".sel").removeClass("sel");
    $("#cubes").children().not(function (index) {
      return this.style["background-color"] == "green";
    }).addClass("sel");
  }

  function notYellow() {
    $(".sel").removeClass("sel");
    $("#cubes").children().not(function (index) {
      return this.style["background-color"] == "yellow";
    }).addClass("sel");
  }
</script>