Q:

Change the format of the text in a cell to striketrough

Below is the code which would do some basic conditional formatting of a range of cells.  This code sets the background color to red.  Now I want to change the text format to Striketrough.  But as the documentation here says, setStrikethrough is a function in the class Text.  Now how could I implement this in the example below? 
Here is my scenario:
function onEdit() {
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sheet = ss.getSheetByName('Actiepunten');
  var rows = sheet.getRange('a1:j');
  var numRows = rows.getNumRows();
  var values = rows.getValues();

  for (var i = 0; i <= numRows - 1; i++) {
    for (var x in values[i]){
      if (values[i][x] == 'Done' || values[i][x] == 'done'){
        var n = i + 1;
        var Range = sheet.getRange('a'+n+':f'+n).setBackgroundColor('red');

     }
   } 
 }
 };

A:

Look at the spreadsheet app documentation. 
https://developers.google.com/apps-script/reference/spreadsheet/range#setFontLine(String)
.setFontLine("line-through");

