Check if a value is falsy. The word "falsy" means the value is one of undefined, null, false, 0, NaN or an empty string "".

isFalsy.js

// Check if a value is falsy. This is, its value is one of undefined, null, false, 0, NaN or an empty string "".
// Also, you can use the Boolean function to convert the value.
function isFalsy(o) {
    return !o;
}