JSFiddle - React, Tailwind, and code Playground

HTML

<div class="sum">
sum
</div>

JavaScript

var userNum=10;

var  increase = 0;

 var totalSum = 0;

 var expression = "+";

   $('.sum').text("the sum of the odd numbers are:");
  // while the increase is less than the userNum , the increase will 
   //increase by one
   var txt=[];
   while(increase < userNum){
  increase++
   // if the increase is odd , it will be added to the totalSum
    if(increase % 2 === 0){}
    else{
         txt.push(increase);
            totalSum = totalSum + increase
    }    
}
$(".sum").text(txt.join("+") + "=" + totalSum);