Sortable - Update Existing Array - jQuery

Question

I have an existing array of elements, example:

arr=[{name:1,data:xyz},{name:2,data:abc},{name:3, data:lmn}; {name:4,data:opq}]

This items are populated according to their name on UI. Example: 1 2 3 4 5

I have implemented Sortable of jQuery. Instead of creating a new array, I wish to update the exiting array arr according to the new position of the elements after the user has done performing the drag & drop operation on the above elements.

User can move elements present inside the array arr and cannot introduce any dragged object from outside the 1 2 3 4 5 elements' list, example: 2 can be moved to 5 or 1 can be moved to 3 etc etc.

Elements HTML:

<ul class= "tree-list">
 <li class="li_class"><span class="span_class"> 1 </span></li>
 <li class="li_class"><span class="span_class"> 2 </span></li>
 <li class="li_class"><span class="span_class"> 3 </span></li>
 <li class="li_class"><span class="span_class"> 4 </span></li>
 <li class="li_class"><span class="span_class"> 5 </span></li>
</ul>

jQuery:

 $(function() {
            var data = $(".tree-list").sortable({
              delay: 150,
              axis: "y",
      
            update: function(event, ui) {
                var index = ui.item.index();
                console.log("Moved to new position: " + index);
                var children = $('ul.tree-list').children()
                // What to do here
           
            })
     
            $( ".tree-list" ).disableSelection();
        });

Array created dynamically:

someFunc(data){
    let htmlString= " <ul class =\"tree-list\" "
    for (let i=0; i<data.length; i++){
        if(typeof(item) === "string"){
          htmlString += "<li class=\" li_class \"" + item + "\">";
                                     }
        else if(typeof(item) === "object"){
          htmlString += "<li>";
          htmlString += "span class=\"span_class\""  
                                     }
           htmlString += "</li>"
                                   }
       }
htmlString += "</ul>";
return (htmlString);

}

Answer 1

I tried to recreate your example using initial array :

what I've done is , at first create data-previndex to store previous index on li position update using start srotable : ( credits to this answer )

then every update, call the array_move (credits to this answer ) which update element on the js array , depending on the previous and current index

See below working snippet :

$(function() {
  let arr = [{name:1,data:"xyz"}, {name:2,data:"abc"}, {name:3, data:"lmn"}, {name:4,data:"opq"}, {name:5,data:"stu"}]
  
  let $treeList = $(".tree-list");
  
  arr.forEach(element => {
    let liNode = `<li class="li_class"><span class="span_class"> ${element.name} </span></li>`
    $treeList.append(liNode);
  })
   
  var data = $(".tree-list").sortable({
    delay: 150,
    axis: "y",
    start: function(e, ui) {
        // creates a temporary attribute on the element with the old index
        // credits to this answer https://stackoverflow.com/questions/1601827/jquery-ui-sortable-how-to-determine-current-location-and-new-location-in-update
        $(this).attr('data-previndex', ui.item.index());
    },

    update: function(event, ui) {
      var newIndex = ui.item.index();
      var oldIndex = $(this).attr('data-previndex');
      
      
      var children = $('ul.tree-list').children()
      // What to do here
      arr = array_move(arr, oldIndex, newIndex);
      console.clear()
      console.log(JSON.stringify(arr));
    }
  });

  $(".tree-list").disableSelection();
});

function array_move(arr, old_index, new_index) {
    if (new_index >= arr.length) {
        var k = new_index - arr.length + 1;
        while (k--) {
            arr.push(undefined);
        }
    }
    arr.splice(new_index, 0, arr.splice(old_index, 1)[0]);
    return arr; 
};

@import url("https://code.jquery.com/ui/1.12.0/themes/smoothness/jquery-ui.css");

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script src="https://code.jquery.com/ui/1.12.0/jquery-ui.min.js"></script>
<ul class="tree-list">
</ul>