title: Comparing two columns, same row, for first value that doesn't match
body: <p>I have two sheets, one is a mirror sheet, "Sheet2," that I use to store the values of the other sheet, "Sheet1."  My goal is to have a function compare the two sheets for differences.  The best way i could think of was by comparing column A from Sheet1 to column A from Sheet2.  I found a few functions that compared 2 columns but it did it looking for values from one column and finding it in the other column.  Or by returning all the values in those cells that had a matching value, regardless of what row it was in. But I don't want the values in the cells, necessarily.  I want to find the first row where the two columns stop matching. I'm fairly new to Javascript so I still can't comprehend the whole <code>for (var j = 0; j &lt; range.length; j++)</code> stuff.  </p>
  
  <p>But I'm sure I will need to know how to use it for this function I need.  Here's what I tried using but instead of giving me row ranges, it gave me an array of values that were the same, if I changed it to <code>if(lookup[i][0]!==range[j][0]){</code>  it gave me all the possible combinations that weren't matching. This is from <a href="https://stackoverflow.com/questions/42044903/google-script-compare-two-columns-and-if-match-paste-matching-value">stackoverflow.com/questions/42044903</a></p>
  
  <pre><code>function findDifference() {
    var ss = SpreadsheetApp.getActiveSpreadsheet();
    var s=ss.getSheetByName("Sheet1")
    var lr=s.getLastRow()
    var lookup = s.getRange(2,1,lr-1,2).getValues();
    var s1=ss.getSheetByName("Sheet2") 
    var lr1=s1.getLastRow()
    var range = s1.getRange(2,1,lr1-1,2).getValues();
    var lookupRange = [];
    for (var i = 0; i &lt; lookup.length; i++) {
       for (var j = 0; j &lt; range.length; j++) {
       var  test=lookup[i][0]
           if(lookup[i][0]!==range[j][0]){
             lookupRange.push([range[j][0],range[j][1],lookup[i][0],lookup[i][1],]);
       }}}
     s1.getRange(10,1,lookupRange.length,4).setValues(lookupRange); 
  }
  </code></pre>
  
  <p>I feel like there's a very similar function for what I'm trying to do that already exists, but I can't seem to find it or come up with how it would work because I'm new and don't know all the tricks.
  Something like:</p>
  
  <pre><code>var ss = SpreadsheetApp.getActiveSpreadsheet();
    var s1=ss.getSheetByName("Sheet1")
    var s2=ss.getSheetByName("Sheet2")
  var ColumnA1 = s1.getRange('A:A').getValues()
  var ColumnA2 = s2.getRange('A:A').getValues()
  var Row = Function()
  ///Some function I can't think of using where
  if(ColumnA1 + Row !== ColumnA2 + Row){
  ???.getRow()
  }
  </code></pre>