Check if object is a 'direct instance' of a class
Check the constructor:
if (!value || value.constructor !== Foo)
throw 'InvalidArgumentException: (...)';
or the prototype of the object (this is more similar to what instanceof does):
if (!value || Object.getPrototypeOf(value) !== Foo.prototype)
throw 'InvalidArgumentException: (...)';
You can use a comparison between Object.getPrototypeOf(yourObj) and Foo.prototype to see if yourObj is exactly an instance of Foo. And you can move up the chain by just continuing to call Object.getPrototypeOf for each level.
Example:
class Foo {}
class Bar extends Foo {}
class Baz extends Bar {}
const foo = new Foo();
const bar = new Bar();
const baz = new Baz();
// For this function:
// - level 0 is self
// - level 1 is parent
// - level 2 is grandparent
// and so on.
function getPrototypeAt(level, obj) {
let proto = Object.getPrototypeOf(obj);
while (level--) proto = Object.getPrototypeOf(proto);
return proto;
}
console.log("bar is a foo:", bar instanceof Foo);
console.log("baz is a foo:", baz instanceof Foo);
console.log("foo is exactly a foo:", getPrototypeAt(0, foo) === Foo.prototype);
console.log("bar is exactly a foo:", getPrototypeAt(0, bar) === Foo.prototype);
console.log("bar is direct child of foo:", getPrototypeAt(1, bar) === Foo.prototype);
console.log("baz is direct child of foo:", getPrototypeAt(1, baz) === Foo.prototype);
console.log("baz is direct child of bar:", getPrototypeAt(1, baz) === Bar.prototype);
console.log("baz is grandchild of foo:", getPrototypeAt(2, baz) === Foo.prototype);You should test if value's internal [[Prototype]] is exactly Foo.prototype. You can get the internal [[Prototype]] with Object.getPrototypeOf :
if ( Object.getPrototypeOf( value ) !== Foo.prototype )
throw "InvalidArgumentException: (...)";