JavaScript isPrototypeOf vs instanceof usage

Imagine you don’t use constructors in your code, but instead use Object.create to generate objects with a particular prototype. Your program might be architected to use no constructors at all:

var superProto = {
    // some super properties
}

var subProto = Object.create(superProto);
subProto.someProp = 5;

var sub = Object.create(subProto);

console.log(superProto.isPrototypeOf(sub));  // true
console.log(sub instanceof superProto);      // TypeError

Here, you don’t have a constructor function to use with instanceof. You can only use subProto.isPrototypeOf(sub).