JSFiddle - React, Tailwind, and code Playground

JavaScript

var num = 1234.56

// Only necessary if you have a longer decimal ...
var result = num.toFixed(2); // 12345.56

result = numberWithSpace(result);

alert(result);

function numberWithSpace(x) {
    return x.toString().replace(/\B(?=(\d{3})+(?!\d))/g, " ");
}