TypeError: "x" is not a non-null object

TypeError: Property description must be an object: x (V8-based)
TypeError: Property descriptor must be an object, got "x" (Firefox)
TypeError: Property description must be an object. (Safari)

TypeError: Invalid value used in weak set (V8-based)
TypeError: WeakSet value must be an object, got "x" (Firefox)
TypeError: Attempted to add a non-object value to a WeakSet (Safari)

An object is expected somewhere and wasn't provided. null is not an object and won't work. You must provide a proper object in the given situation.

When methods like Object.create() or Object.defineProperty() and Object.defineProperties() are used, the optional descriptor parameter expects a property descriptor object. Providing no object (like just a number), will throw an error:

Object.defineProperty({}, "key", 1);
// TypeError: 1 is not a non-null object

Object.defineProperty({}, "key", null);
// TypeError: null is not a non-null object

A valid property descriptor object might look like this:

Object.defineProperty({}, "key", { value: "foo", writable: false });

WeakMap and WeakSet objects store object or symbol keys. You can't use other types as keys.

const ws = new WeakSet();
ws.add("foo");
// TypeError: "foo" is not a non-null object

Use objects instead:

ws.add({ foo: "bar" });
ws.add(window);

• Object.create()
• Object.defineProperty(), Object.defineProperties()
• WeakMap, WeakSet