TypeError: can't assign to property "x" on "y": not an object

Ошибка строгого режима JavaScript "can't assign to property" ("невозможно присвоить свойство") происходит в тот момент, когда вы пытаетесь создать свойство примитивного типа данных (такого как символ, строка, число или булевое значение). Примитивные типы данных не могут содержать никаких свойств.

Message

TypeError: can't assign to property "x" on {y}: not an object> (Firefox)
TypeError: Cannot create property 'x' on {y} (Chrome)

Error type

TypeError.

What went wrong?

In Strict_mode, a TypeError is raised when attempting to create a property on primitive value such as a symbol (en-US), a string, a number or a boolean. Primitive values cannot hold any property (en-US).

The problem might be that an unexpected value is flowing at an unexpected place, or that an object variant of a String or a Number is expected.

Examples

Invalid cases

js
"use strict";

var foo = "my string";
// The following line does nothing if not in strict mode.
foo.bar = {}; // TypeError: can't assign to property "bar" on "my string": not an object

Fixing the issue

Either fix the code to prevent the primitive from being used in such places, or fix the issue is to create the object equivalent Object.

js
"use strict";

var foo = new String("my string");
foo.bar = {};

See also