Google Apps Script for Spreadsheets - Find the relative row number within a range that has a a cell with given target value - Range in A1 Notation starting

gistfile1.txt

function findRowNumberForCellWithValue(targetValue, rangeA1Notation, sheet) {
  var range = sheet.getRange(rangeA1Notation);
  var values = range.getValues()
  
  for (var i = 0; i < values.length; i++) {
    if (values[i][0] == targetValue) {
      return i+1;
    }    
  }  
}

Example: Getting the line number of the first empty cell on first column

var spreadsheet = SpreadsheetApp.getActiveSpreadsheet();
var sheet = spreadsheet.getSheetByName('MySheetName');

var emptyLineNumber = findRowNumberForCellWithValue('', 'A:A', sheet);

This is very useful for many logger scripts where you have to fill the last line with the updated value.