TypeError: can't redefine non-configurable property "x"

The JavaScript exception "can't redefine non-configurable property" occurs when it was attempted to redefine a property, but that property is non-configurable.

Message

TypeError: Cannot modify non-writable property {x} (Edge)
TypeError: can't redefine non-configurable property "x" (Firefox)
TypeError: Cannot redefine property: "x" (Chrome)

Error type

TypeError

What went wrong?

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.

Examples

Non-configurable properties created by Object.defineProperty

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

var 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. 

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

See also