Question

Consider such an object with a prototype chain:

var A = {};
var B = Object.create(A);
var C = Object.create(B);

How to check in runtime if C has A in its prototype chain?

instanceof doesn’t fit as it’s designed to work with constructor functions, which I’m not using here.

Answer 1

My answer will be short…

You could use the isPrototypeOf method, which will be present in case your object inherits from the Object prototype, like your example.

example:

A.isPrototypeOf(C) // true
B.isPrototypeOf(C) // true
Array.prototype.isPrototypeOf(C) // false

More info can be read here: Mozilla Developer Network: isPrototypeOf