JSFiddle - React, Tailwind, and code Playground

JavaScript

var userInput = "+54,568,568.14589";
var decimalPoints = 3;
var convertedValue;

var indexP = userInput.indexOf("+");
//getting rid of commas
var value = userInput.replace(/,/g , "");

value =parseFloat(value).toFixed(decimalPoints);
convertedValue = value.toString(); 
if(indexP == 0){
console.log('Converted Value: +'+convertedValue);
}
else{
console.log('Converted Value: '+convertedValue);
}
console.log('Actual Value: '+userInput);