examples/intro/mixing.js
"use strict";

var a = "23";
var b = "19";
console.log(a + b); // "2319"


var x = 23;
var y = "19";
console.log(x + y); // "2319"

var p = 23;
var q = 19;
console.log(p + q); // 42

In a nutshell: Don't do that!