JSFiddle - React, Tailwind, and code Playground

HTML

<input type="button" value="Run Examples" onClick="run()" style="width: 200px; height: 50px" />

JavaScript

function run() {
    var x;
    if(x) {
        alert("this will never show because x is undefined");
    } else {
        alert("this will always show because x is undefined");
    }
    
    var y = "something";
    if(y) {
        alert("this will always show because y has a value");
    }
}