Message
TypeError: "x" is not a non-null object (Firefox) TypeError: Property description must be an object: "x" (Chrome) TypeError: Invalid value used in weak set (Chrome)
Error type
What went wrong?
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.
Examples
Property descriptor expected
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 require object keys
WeakMap and WeakSet objects store object keys. You can't use other types as keys.
var ws = new WeakSet();
ws.add('foo');
// TypeError: "foo" is not a non-null object
Use objects instead:
ws.add({foo: 'bar'});
ws.add(window);