Google Apps Script: How to find column number of specific value in array?

What I'm trying to achieve is to get the column number of a specific cell. If the cell value in the array equals to the value of today's date, then give back the column number of that cell.

dateArrayD = 1 row containing all the dates from January 1 to December 31, formatted

dateTodayD = the date today, formatted

So if dateTodayD equals dateArrayD, then dateCol would be the column number. I simply can't find a solution for this.

for(var z = 0; z < dateArrayD.length; z++){
    if(dateTodayD !== dateArrayD[0][z]){
      var dateCol = z;
    } // end if
  } // for end