JSFiddle - React, Tailwind, and code Playground

JavaScript

// Default function parameters

function test(x) {
    var param = x || 0;
    return param + 1;
}

function isDef(obj) {
    return typeof obj !== "undefined" && obj !== null;
}

function print(key, val) {
    if (isDef(key)) {
        if (isDef(val)) {
            document.body.innerHTML += "<p>Key: " + key + " Val: " + val + "</p>";
        } else {
            document.body.innerHTML += "<p>" + key + "</p>";
        }
    }
}

print(test())
print(test(5));
print(test(var));