How to use JavaScript Date object to find corresponding data for a particular month in Apps Script

So I am currently making an expense tracker, and there is a feature that I'd like to implement.

So basically:

In this spreadsheet, the first two dates are automatically generated by the JavaScript Date object, while the rest aren't because I wanted to give an example of what my feature would do.

So currently, I have a custom function in Apps Script, one that returns how much a person has spent on a particular brand, like this (this is an HTML sidebar):

And returns this (although the numbers might be a bit off since I changed some of the data):

function perCentBrand(categ){
  var sh = SpreadsheetApp.getActiveSpreadsheet().getActiveSheet();
  var values = sh.getRange(2,1,sh.getLastRow()-1,sh.getLastColumn()).getValues();
  var total = 0;
  var sum = 0;
  values.forEach(function(row){
    total+=row[1];
    if (row[6]==categ){sum+=row[1]}
  })
  var val = "You spent a total of " + sum + " on " + categ + " out of " + total + " ." + " Additionally, " + (sum/total)*100 + "%"  + " of your income has been spent on " + categ; 
  var ui = SpreadsheetApp.getUi();
  ui.alert(val)
}

The custom function is run in the HTML file like this:

  <script>
    function runFunc(){
      var brand = document.getElementById("brand").value;
      google.script.run.perCentBrand(brand);
    }

  </script>

and:

<form onsubmit="runFunc()">

Is there any way I can implement a similar feature, where for example, if I input the number 1 (corresponding to January), in an HTML input, it would return to me in UI alert the date, Amount Spent, and the Clothing brand?

I am new to JS and Apps Script but here is what I've tried:

function dateChecker(monthVal){
  var sh = SpreadsheetApp.getActiveSpreadsheet().getActiveSheet();
  var values = sh.getRange(2,1,sh.getLastRow()-1,sh.getLastColumn()).getValues();
  let date = new Date();
  let monthVal = date.getMonth();
  values.forEach(function(row){
    total+=row[1];
    if (row[6] && row[1] && row[5] == monthVal){sum+=row[1]}
  })
  var val = "In the month of" + monthVal + "here is what you have spent" + row[6] + row[1] + row[5];
  var ui = SpreadsheetApp.getUi();
  ui.alert(val)
}

Probably, basically you can just add one more argument month in your function:

function perCentBrand(categ, month) {
    ...

And one more condition row[0].getMonth() + 1 == month:

if (row[6] == categ && row[0].getMonth() + 1 == month) { sum += row[1] }

It will give you the sum for a given month and brand. It supposes that year is a current year always.

And of course it's need to add the input area with ID="month" in your form as well and use it in the script about this way:

<script>
    function runFunc(){
      var brand = document.getElementById("brand").value;
      var month = document.getElementById("month").value;
      google.script.run.perCentBrand(brand, month);
    }
</script>

I don't know how your HTLM-code looks like so it's up to you to add the input area to somewhere.

Date.getMonth() returns you a number of the month from a date object, where 0 is January, 1 is February, etc.