Instanceof equivalent for Object.create and prototype chains

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

Answer 2

You could iterate back through the prototype chain by calling Object.getPrototypeOf recursively: http://jsfiddle.net/Xdze8/.

function isInPrototypeChain(topMost, itemToSearchFor) {     var p = topMost;      do {          if(p === itemToSearchFor) {             return true;         }          p = Object.getPrototypeOf(p); // prototype of current      } while(p); // while not null (after last chain)      return false; // only get here if the `if` clause was never passed, so not found in chain }