Fix bug when try customize the exported data

[enniosousa]

I need remove duplicated rows that occurs when one or more columns are not displayed (ColVis) use the callback customizeData is the best way extending the button and using configuration, but it isn't overwrite the variable, I can only read the value

$.extend(true, $.fn.dataTable.ext.buttons, {
    separatedValues: {
        className: 'buttons-sv-export',
        text: '<i class="fa fa-file-excel-o"></i> separatedValues',
        exportData: {
            modifier: {
                selected: true
            },
            columns: ':visible'
        },
        exportOptions: {
            customizeData : function(data){
                var bodySeen = {};
                var bodyDistincted = [];
                var j = 0;
                for (var i = 0; i < data.body.length; i++) {
                    var item = data.body[i];
                    if (bodySeen[item] !== 1) {
                        bodySeen[item] = 1;
                        bodyDistincted[j++] = item;
                    }
                }

                data.body = bodyDistincted;

                return data;
            }
        },
        extend: 'csvHtml5',
    },
});

[DataTables]

What you are seeing is actually expected - it is expected to mutate the data rather than replace it. So for example you might use splice to remove an item from the array.

That said, I don't really any harm in this. Going to leave open for the moment to think about it and also because the docs would need to be updated.

[AllanJard]

Been looking at this again, and almost committed the change (although looking for an undefined return as well) but decided that I want to encourage anyone doing this to mutate the object and arrays rather than define their own, particularly with the new structure properties in the data.