commonGAS.js

if ( cell.length || cell ) // testing if a cell contains something other than an empty string or 0

// parsing through sheet - best practice, grab entire sheet and loop through array
data = sht.getDataRange().getValues();
for ( var r = 0; r < data.length; r += 1 ) { // rows are looped through first
  for ( var c = 0; c < data[0].length; c += 1 ) { // columns are next
    data[r][c];
  }
}

// when pushing raw data back to the sheet (which doesn't contain any formulas - otherwise they will be overwritten):
sht.getRange( 1, 1, data.length, data[0].length ).setValues( data );

// from http://stackoverflow.com/a/1830844
function isNumber( n ) {
  return !isNaN(parseFloat(n)) && isFinite(n);
}

// http://stackoverflow.com/a/10589791
function isDate( d ) {
  return d instanceof Date && !isNaN(d.valueOf());
}

// from http://stackoverflow.com/a/9436948/1618944
function isString( s ) {
  return typeof s == 'string'  ||  s instanceof String; 
}

// if you have formulas it is best to have them behind frozen rows and columns. Then 
// when you want to paste back in the raw data you can remove the frozen elements from
// the 2-d array and paste the data back in without interferring with the frozen formulas
function removeFrozens( data, fr, fc ) {
  data.splice( 0, fr );
  for ( var r = 0; r < data.length; r += 1 ) {
    data[r].splice( 0, fc );
  }
  return data;
}

data = removeFrozens( data, fr, fc );
sht.getRange( fr + 1, fc + 1, data.length, data[0].length ).setValues( data );


// creating a menu
// https://developers.google.com/apps-script/articles/defining_menus
function onOpen() {
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var menuEntries = [ {name: "Run a Function", functionName: "runThisFunction"},
                      null, // if you want a nice horizontal line
                      {name: "Do Something", functionName: "runThatFunction"} ];
  ss.addMenu("ACC", menuEntries);
}

// delete everything except for the frozen ROWS
// handy for when you need to append new data into a sheet
data = sht.getDataRange().getValues();
fr = sht.getFrozenRows();
data.splice( fr );

// copying an array and passing it as a value to a function where you DON'T want the original
// array to be modified - http://stackoverflow.com/a/14491446/1618944
function( origArray ) {
  var newArray = origArray.slice(0);
  return newArray;
}