🧑‍🎓 Optional

If you want to allow null and undefined as allowed values, you can use optional() function to transform Predicate into a Predicate that allows those values:

const { asVerificable, optional, isString, ensure } = require("verifica");

function sayName(name) {
    const vname = asVerificable(name);
    
    const isOptionalString = optional(isString);
    ensure(vname, isOptionalString);
    
    if (name == null) {
        console.log("Hello, anonymous!");
    } else {
        console.log(`Hello, ${name}!`);
    }
}