JSFiddle - React, Tailwind, and code Playground

JavaScript

var str = 'This, is a test.'; 
alert( removeLastComma(str) ); // should remain unchanged

var str = 'This, is a test,'; 
alert( removeLastComma(str) ); // should remove the last comma

var str = 'This is a test,          '; 
alert( removeLastComma(str) ); // should remove the last comma

function removeLastComma(strng){
    
var n=strng.lastIndexOf(",");
var a=strng.substring(0,n) 
return a;
}