tooltip: {
     crosshairs: [true, true],
     shared: true,
     useHTML: true,
    formatter: function() {

            var s = [];
            s.push('<table><tr><td style="text-align:right;" colspan="3"><b>' +
             this.x + '</b></td></tr>');
            $.each(this.points, function(i, point) {
                s.push('<tr><td style="text-align: right;">'+
                              '<b><span style="color:'+point.series.color +'">u25CF</span></b>'+
                           '</td>'+
                           '<td style="text-align: right;"><b>'+point.series.name +' : </b></td>'+
                           '<td><b>' + point.y+'</b></td>'+
                       '</tr>');
            });

            s.push('<tr><td style="text-align:right;" colspan="3"><b>تعداد خبر : ' +
             this.points[0].point.NumberNews + '</b></td></tr></table>');
            return s;
    }
},

var s = [];
// ...
return s;

var s = [];
// ...
return s.join('');

tooltip: {
     crosshairs: [true, true],
     shared: true,
     useHTML: true,
     formatter: function() {

        var s = [];
        s.push('<table><tr><td style="text-align:right;" colspan="3"><b>' +
         this.x + '</b></td></tr>');
        $.each(this.points, function(i, point) {
            s.push('<tr><td style="text-align: right;">'+
                          '<b><span style="color:'+point.series.color +'">u25CF</span></b>'+
                       '</td>'+
                       '<td style="text-align: right;"><b>'+point.series.name +' : </b></td>'+
                       '<td><b>' + point.y+'</b></td>'+
                   '</tr>');
        });

        s.push('<tr><td style="text-align:right;" colspan="3"><b>تعداد خبر : ' +
         this.points[0].point.NumberNews + '</b></td></tr></table>');
        return s.join(''); //This will removed comma's, if you want to put an string separator just insert it inside the return//
    }
},