Google Apps Script to combine data from different sheets (used in http://mashe.hawksey.info/?p=13130)

gistfile1.js

function combineData(){
 var doc = SpreadsheetApp.getActiveSpreadsheet();
 var sheets = doc.getSheets(); // get all the sheets
 var outSheet = doc.getSheetByName("combined"); // set where we want to write the results
 for (i in sheets){ // loop across all the sheets
   if (sheets[i].getSheetName().substring(0,9) == "followers"){ // if sheetname starts with 'follower' then 
     var target = sheets[i].getSheetName().substring(12); // extract users name for target column
     var data = getRowsData(sheets[i]); // get extisting data from current sheet
     for (j in data){
       data[j]["target"] = target; // create a target column with the users name
     }
     insertData(outSheet, data); // insert data in 'combined' sheet
   }
 }
}

Where is the insertData function referenced here?