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HTML 

              
                .controls
  %button#prepend PREPEND CHANNEL
  %button#append APPEND CHANNEL
  %button#reset RESET CHANNELS
.channels
  .channel#c1
    #block
!

CSS 

              
                .controls
  width: 720px
  margin: 5px auto 0
  button
    position: relative
    display: inline-block
    background: green
    border: none
    color: white
    font-size: 16px
    margin: 0 20px 0 0
    cursor: pointer
    &#reset
      float: right
      margin-right: 0
.channels
  position: relative
  width: 720px
  margin: 5px auto
  background: black
.channel
  position: relative
  height: 50px
  width: 720px
  background: #b2b2b2
  margin: 0 0 2px
  &.selected
    background: #dddddd
  #block
    top: 0
    left: 0
    position: relative
    display: block
    height: 50px
    width: 100px
    background: green
    vertical-align: middle
!

JS 

              
                let block = document.getElementById('block'),
    chContainer = document.querySelector('.channels'),
    allChannels = Array.from(document.querySelectorAll('.channel')),
    parentChannel = block.parentNode,
    draggable;

function setDrag() {
  if (draggable) {
    draggable.kill();
  }
  draggable = Draggable.create(block,{
    type:"top,left",
    bounds: '.channels',
    lockAxis: true,
    dragClickables: false,
    snap: {
      left: function(endVal) {
        return Math.round(endVal);
      }
    },
    onDrag: function(e) {
      for( let ch of allChannels ) {
        if (this.hitTest(ch, "50%")) {
          $('.channel').removeClass('selected');
          ch.classList.add('selected');
        }
      }
    },
    onRelease: function() {
      for( let ch of allChannels ) {
        if (this.hitTest(ch, "50%")) {
          $('.channel').removeClass('selected');
          ch.appendChild(block);
          TweenMax.set(this.target,{top: 0});
        }
      }
    }
  })[0];
}

function setResizable() {
  $(block).resizable({
    containment: 'parent',
    handles: 'e,w',
    create: function() {
      $('.ui-resizable-handle').attr('data-clickable',true);
      $('.ui-resizable-handle').on('mousedown', function(){
        draggable[0].disable();
      });
    },
    stop: function() {
      draggable[0].enable();
    }
  })
}

setResizable();
setDrag();

function addChannel(dir) {
  let ch = document.createElement('div');
  ch.id = `c${allChannels.length+1}`;
  ch.className = 'channel added';
  if( dir == 'prepend' ) {
    chContainer.insertBefore(ch,allChannels[0]);  
  } else {
   chContainer.appendChild(ch);
  }
  allChannels = Array.from(document.querySelectorAll('.channel'));
}

function resetChannels() {
  $('.channel.added').remove();
  allChannels = Array.from(document.querySelectorAll('.channel'));
  if( $('#block').length == 0 ) {
    block = document.createElement('div');
    block.id = 'block';
    allChannels[0].appendChild(block);
  }
  parentChannel = block.parentNode;
  setDrag();
}

$('.controls button').on('click', function(){
  if( this.id == 'reset' ) {
    resetChannels();
  } else {
    addChannel(this.id); 
  }
});
!
999px

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