How to sort Datatable by days in string value

Here are two approaches:

Use a Column Renderer

You can create a mapping from day names to numbers:

var days = { 'Monday': 1, 'Tuesday': 2, 'Wednesday': 3, 'Thursday': 4, 'Friday': 5, 'Saturday': 6, 'Sunday': 7 };

You can then use that mapping when you create your DataTable.

Here is my test data in my HTML table:

    <table id="example" class="display dataTable cell-border" style="width:100%">
        <thead>
            <tr>
                <th>Name</th>
                <th>Day</th>
            </tr>
        </thead>
        <tbody>
            <tr>
                <td>Tiger Nixon</td>
                <td>Monday</td>
            </tr>
            <tr>
                <td>Garrett Winters</td>
                <td>Tuesday</td>
            </tr>
            <tr>
                <td>Ashton Cox</td>
                <td>Wednesday</td>
            </tr>
            <tr>
                <td>Cedric Kelly</td>
                <td>Thursday</td>
            </tr>
            <tr>
                <td>Airi Satou</td>
                <td>Friday</td>
            </tr>
            <tr>
                <td>Brielle Williamson</td>
                <td>Saturday</td>
            </tr>
            <tr>
                <td>Herrod Chandler</td>
                <td>Sunday</td>
            </tr>
        </tbody>
    </table>

Here is my DataTable definition:

$('#example').DataTable( {
  "columnDefs": [ {
    "targets": 1,
    "render": function ( data, type, row, meta ) {
      if (type === 'sort') {
        return days[data];
      } else {
        return data;
      }
    }
  } ]
} );

For the second column (index = 1), I use a render function to map from the name of the day to an integer. DataTables will use this integer for sorting operations (type === 'sort'). Otherwise it will use the name of the day.

The days[data] expression is used to look up the relevant number from my days variable.

The data looks like this when it is sorted by day name:

Warning:

When you use a renderer which produces numeric sort data from data which is alphanumeric, you do have to be careful. Even though numbers are used for sorting, they are treated as alphanumeric. In our case, this makes no difference, because the string values "1" through "7" are sorted the same way as the integer values 1 through 7.

But if you wanted to do something similar with the months of the year, then you would run into problems, as October (10), November (11) and December (12) would potentially be mis-sorted.

One fix for this is to force the column to be treated as if it contains numeric data by default: "type": "num",. Credit to this answer for highlighting this potential issue.

(Forcing the return value to be an integer does not help: return parseInt(days[data]);).

Delegated Sorting

An alternative approach is to populate the relevant number into an extra column when you load your data into the table.

In your DataTable definition, you can hide this column:

"columnDefs": [
  { "visible": false, "targets": 2 }
]

Then you can use the DataTables orderData option to delegate sorting from the visible "day name" column to the hidden "day number" column:

"columnDefs": [
  { "visible": false, "targets": 2 },
  { "orderData": [ 1 ],    "targets": 2 }
]

This tells DataTables to use the data in column index 2 when you sort on column index 1.