JS: Object.prototype.isPrototypeOf

objA.isPrototypeOf(objB)

• Return true if objA is in Prototype Chain of objB. Else false.
• If objA is objB, return false

// example of isPrototypeOf

const xaa = {};
const xbb = {};

// make xaa the parent of xbb
Object.setPrototypeOf(xbb, xaa);

console.log(xaa.isPrototypeOf(xbb));

// isPrototypeOf returns true for grand parents too
const x1 = {};
const x2 = Object.create(x1);
const x3 = Object.create(x2);
const x4 = Object.create(x3);
console.log(x1.isPrototypeOf(x4));
// true

// example of isPrototypeOf on same objects
const xx = {};
console.log(xx.isPrototypeOf(xx) === false);