The JavaScript strict mode exception "can't assign to property" occurs when attempting to create a property on primitive value such as a symbol, a string, a number or a boolean. Primitive values cannot hold any property.
Message
TypeError: can't assign to property "x" on {y}: not an object
(Firefox)
TypeError: Cannot create property 'x' on {y} (Chrome)
Error type
What went wrong?
In Strict_mode
, a TypeError
is raised when attempting to create a property on primitive value such as a symbol, a string, a number or a boolean. Primitive values cannot hold any property.
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
'use strict';
var foo = "my string";
// The following line does nothing if not in strict mode.
foo.bar = {}; //
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
.
'use strict'; var foo = new String("my string"); foo.bar = {};