getColByName.js

// get column by the content in it - first row only
function getColByName(columnName) {
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sheet = ss.getSheets()[0];
  var range = sheet.getRange(1, 1, 1, sheet.getLastColumn());
  var values = range.getValues();

  for (var row in values) {
    for (var col in values[row]) {
      if (values[row][col] == columnName) {
        var num = Number(col) + 1;
        return num.toFixed();
      }
    }
  }
}