JSFiddle - React, Tailwind, and code Playground

JavaScript

function testFoo(foo) {
    console.group();
    if (foo) {
        console.log(foo, "truthy");
    } else {
        console.log(foo, "falsey");
    }
    
    if (!!foo) {
        console.log(!!foo, "truthy");
    } else {
        console.log(!!foo, "falsey");
    }
    console.groupEnd();
}

testFoo();

testFoo('');

testFoo(null);

testFoo('0');

testFoo(0);

testFoo('1');

testFoo(1);

testFoo(true);

testFoo(false);