I need to find a way to create a JavaScript object with null prototype.
I'm not allowed to use the Object.create function.
I tried instantiating a constructor like new Constructor(), but the returned object always has a non-null prototype, even if Constructor.prototype === null.
Such an object already exists, it's Object.prototype, so your code is as simple as
x = Object.prototype
but you cannot create a new object like this, because new always sets the proto to an object:
If Type(proto) is not Object, set the [[Prototype]] internal property of obj to the standard built-in Object prototype object as described in 15.2.4. @ http://ecma-international.org/ecma-262/5.1/#sec-13.2.2
You can manipulate __proto__ directly
a = {}
a.__proto__ = null
var a = {};
a.prototype = null;
alert(a.prototype);
The usual way to create an object that inherits from another without Object.create is instantiating a function with the desired prototype. However, as you say it won't work with null:
function Null() {}
Null.prototype = null;
var object = new Null();
console.log(Object.getPrototypeOf(object) === null); // false :(But luckily, ECMAScript 6 introduces classes. The approach above won't directly work neither because the prototype property of an ES6 class is non-configurable and non-writable.
However, you can take advantage of the fact that ES6 classes can extend null. Then, instead of instantiating, just get the prototype of the class:
var object = (class extends null {}).prototype;
delete object.constructor;
console.log(Object.getPrototypeOf(object) === null); // true :)