JS: Show Prototype Chain 📜

Here is a function that returns any object's Prototype Chain as array.

/*
xah_get_proto_chain(obj)
Take any object, returns a array, the order of elements shows the proto chain. First element is obj itself, last element is root.
http://xahlee.info/js/js_show_prototype_chain.html
Version: 2020-06-25
 */
const xah_get_proto_chain = (x) => {
 const result = [x];
 let t = x;
 while ((t = Reflect.getPrototypeOf(t)) !== null) result.push(t);
 return result;
};

// test

const x1 = { k: 1 };
const x2 = Object.create(x1);
x2.k = 2;
const x3 = Object.create(x2);
x3.k = 3;

console.log(xah_get_proto_chain(x3));
// [ { k: 3 }, { k: 2 }, { k: 1 }, [Object: null prototype] {} ]

// s------------------------------
// standard builtin objects

console.log(xah_get_proto_chain([3, 4]));
// [ [ 3, 4 ], Object(0) [], [Object: null prototype] {} ]

console.log(xah_get_proto_chain({ p: 1 }));
// [ { p: 1 }, [Object: null prototype] {} ]

console.log(xah_get_proto_chain(function f() {
 return 3;
}));
// [ [Function: f], {}, [Object: null prototype] {} ]

console.log(xah_get_proto_chain(new Date()));
// [ 2026-02-03T17:35:39.302Z, {}, [Object: null prototype] {} ]

// note, nodejs prints Object.prototype as {}, same as a newly created object, even though they are different object

console.log(Object.prototype);
// [Object: null prototype] {}

// similarly, Array.prototype prints as [], etc.