JSFiddle - React, Tailwind, and code Playground
JavaScript
var numero = 39.8 - 28.2;
var partes = (numero + '').split('.');
var parteCorrigida = partes[1].slice(0, 2);
var numeroFinal = [partes[0], parteCorrigida].join('.')
console.log(numeroFinal); //11.59