IF/ELSE statement in Javascript problems

I am new here and new to Javascript, I have looked through many of the questions and answers here relating to using IF/ELSE but I still can’t seem to get what I have working.
What I have is a page with a user input, so based upon the number entered I want to do one calculation if TRUE and another if FALSE. I would be grateful of any help or guidance. Script below:

<script language="javascript" type="text/javascript">
function calculate()

if ($("#lvl").val() < 50)
{

let lvl_fld={}

lvl_fld.level = Math.floor($("#lvl").val() * 1.5 + 4.5)
$("#flds").val(lvl_fld.level);

let total = Math.floor(lvl_fld.level); 

$("#total_value").text(total);
}
else
{
let lvl_fld={}

lvl_fld.level = Math.floor($("#lvl").val() * 2 + 8)
$("#flds").val(lvl_fld.level);

let total = Math.floor(lvl_fld.level); 

$("#total_value").text(total);

}

$(function()
{
$(".qty").on("change keyup",calculate)
})

</script>