JSFiddle - React, Tailwind, and code Playground

JavaScript

//Example 1

var y = 10;
var x = 4; //user input, temp value.

x += y;
document.write(x);

//Example 2

var y = 10;
var x = y;

x += y;
document.write(x);

//Example 3

var y = 10;
var x = 4; //user input

var n = x + y;
document.write(n);