TypeError: Cannot redefine property: "x" (V8-based)
TypeError: can't redefine non-configurable property "x" (Firefox)
TypeError: Attempting to change value of a readonly property. (Safari)

It was attempted to redefine a property, but that property is non-configurable. The configurable attribute controls whether the property can be deleted from the object and whether its attributes (other than writable) can be changed. Usually, properties in an object created by an object initializer are configurable. However, for example, when using Object.defineProperty(), the property isn't configurable by default.

The Object.defineProperty() creates non-configurable properties if you haven't specified them as configurable.

const obj = Object.create({});
Object.defineProperty(obj, "foo", { value: "bar" });

Object.defineProperty(obj, "foo", { value: "baz" });
// TypeError: can't redefine non-configurable property "foo"

You will need to set the "foo" property to configurable, if you intend to redefine it later in the code.

const obj = Object.create({});
Object.defineProperty(obj, "foo", { value: "bar", configurable: true });
Object.defineProperty(obj, "foo", { value: "baz", configurable: true });

• [[Configurable]]
• Object.defineProperty()