DataTables Excel style based on cell class

Question

I'm using DataTables plugin to export a monthly calendar view; I need to set a cell style inside the excel file based on the class of the corrisponding cell in the DataTables calendar view.
I know how to style the exported excel file using the customize: function( xlsx, index ) {} however I'm not able to find, in the examples I saw on the forum, a way to set the style of the excel cell based on the class of the corrispondig cell in the DataTables view.
I have created my own xml style like this:

customize: function( xlsx, index ) {
  var new_style = '<?xml version="1.0" encoding="UTF-8"?>'+
  '<styleSheet xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main" '+
  'xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" '+
  'xmlns:x14ac="https://schemas.microsoft.com/office/spreadsheetml/2009/9/ac" mc:Ignorable="x14ac">'+
    '<numFmts count="2">'+
      '<numFmt numFmtId="164" formatCode="0.0" />'+
      '<numFmt numFmtId="165" formatCode="\d\d\d" />'+
    '</numFmts>'+
    '<fonts count="4" x14ac:knownFonts="1">'+

    ...... a lot of stuff here ....

    '<extLst>'+
      '<ext xmlns:x14="https://schemas.microsoft.com/office/spreadsheetml/2009/9/main" uri="{EB79DEF2-80B8-43e5-95BD-54CBDDF9020C}">'+
        '<x14:slicerStyles defaultSlicerStyle="SlicerStyleLight1" />'+
      '</ext>'+
    '</extLst>'+
  '</styleSheet>';

This is a styles.xml as you can find iside an .xlsx file if you change the extension to .zip and than unzip it. To apply the styles to the excel cell I'm doing:

  xlsx.xl['styles.xml'] = $.parseXML(new_style);
  var sheet = xlsx.xl.worksheets['sheet1.xml'];

  $('row:first c', sheet).attr( 's', '1' );
  $('row:eq(1) c', sheet).attr( 's', '2' );
  $('row:eq(2) c', sheet).attr( 's', '3' );
}

What I need to do is something like:

     $('row:eq(3) c', sheet).hasClass('custom').attr( 's', '1' ); //not working

or:

    $('row c[r^="B"]', sheet).each( function () {
       if ( $(this).hasClass('custom') ) {
       $(this).attr( 's', '4' );
      }
    }); // not working

Basically I'm working on a row of cells (more than 30, so I have AA, AB, AC and so on) and i need a method to discriminate some of them to add a different style, as you can see the header has 31 cells with calendars day/name and i would like the colums with Saturday and Sunday to be with a gray background like they are in the datatable table.

This is the datatable:

And this is the excel file so far, i need the Sab and Dom columns to be gray

UPDATE * with @andrewjames solution and @georg solution for double letters posted here Convert numbers to letters beyond the 26 character alphabet

function colName(n) {
  var ordA = 'A'.charCodeAt(0);
  var ordZ = 'Z'.charCodeAt(0);
  var len = ordZ - ordA + 1;
  var s = "";
  while(n >= 0) {
    s = String.fromCharCode(n % len + ordA) + s;
    n = Math.floor(n / len) - 1;
  }
  return s;
}

var cellIndexes = tabellaOre.cells(".Sab, .Dom").indexes();

for (var i = 0; i < cellIndexes.length; i++) {
  var cellIndex = cellIndexes[i];
  var tblRow = cellIndex['row']+4; //changed to my needs
  var tblCol = cellIndex['column']; //removed +1
  // var xlCol = String.fromCharCode(64 + tblCol); changed with follow
  var xlCol = colName(tblCol);

  // .... previous stuff here, it was already in a for() loop, so still working

  $('row c[r='+xlCol+tblRow+']', sheet).attr('s','12');
}

and this is the result:

As @andrewjames correctly says in his anwer:

My naive implementation will fail for more than 26 columns:

The colName(n) function solved the problem.
One last step would be to style the cells with thick borders with their own style, but I can consider this as solved.

Answer 1

Assumptions:

It sounds like you already have your embedded styles.xml customized the way you want it, and you therefore know what style index values to refer to, from its <cellXfs> section.

It sounds as if the missing piece is knowing which DataTables cells have been given which CSS style classes, so you can select the relevant <cellXfs> indexes for the equivalent Excel cells.

Proposed Approach:

This takes advantage of the fact that the customize function can be passed 3 variables:

• the XML files for the Excel
• an object representing the button object(s)
• the DataTable instance

We use this last one to map classes in the HTML to cells in Excel:

  var table = $('#example').dataTable({
    dom: 'Bfrtip',
    buttons: [
      {
        extend: 'excelHtml5',
        title: '', // no title row
        text: 'Excel',
        customize: function ( xlsx, btnObj, tableInst ){

          var cellIndexes = tableInst.cells(".mycustom").indexes();
          for (var i = 0; i < cellIndexes.length; i++) {
            var cellIndex = cellIndexes[i];
            var tblRow = cellIndex['row']+1; // adjusted from 0 indexed
            var tblCol = cellIndex['column']+1; // adjusted from 0 indexed
            var xlCol = String.fromCharCode(64 + tblCol); // DANGER: fails after Z (26 columns)
            alert('table row ' + tblRow + ' col ' + tblCol
                + ' maps to excel cell ref ' + xlCol + tblRow);
          }
        }
      }
    ]

  });

This doesn't apply any styles, it just shows you how to determine which DataTable cells have been given a specific style, and translates those cell indexes into Excel-style cell references.

So, for the following sample data...

<table id="example" class="display nowrap dataTable cell-border" style="width:100%">
        <thead>
            <tr>
                <th>Head 1</th>
                <th>Head 2</th>
                <th>Head 3</th>
            </tr>
        </thead>
        <tbody>
            <tr>
                <td>Row 1 column 1</td>
                <td>Row 1 column 2</td>
                <td>Row 1 column three</td>
            </tr>
            <tr>
                <td>Row 2 column 1</td>
                <td>Row 2 column 2</td>
                <td>Row 2 column 3</td>
            </tr>
            <tr>
                <td>Row 3 column 1</td>
                <td class="mycustom">Row 3 column 2</td>
                <td>Row 3 column 3</td>
            </tr>
            <tr>
                <td>Row 4 column 1</td>
                <td>Row 4 column 2</td>
                <td>Row 4 column 3</td>
            </tr>
            <tr>
                <td class="mycustom">Row 5 column 1</td>
                <td>Row 5 column 2</td>
                <td>Row 5 column 3</td>
            </tr>
        </tbody>
    </table>

...the above code generates 2 alerts as follows:

table row 3 col 2 maps to excel cell ref B3
table row 5 col 1 maps to excel cell ref A5

You can then use the B3 and A5 values in the selectors you need - for example:

$('c[r=B3] t', sheet).attr( 's', '25' );

Additional notes:

The DataTables cells().indexes() function is described here.

My naive implementation will fail for more than 26 columns:

var xlCol = String.fromCharCode(64 + tblCol);

But it shouldn't be too hard to extend that for Excel columns "AA", "AB", and so on, if needed.

If you want to work at the column (or row) level, instead of the cell level, I have not tried that - but it should be a slightly simpler version of the above.