JavaScript Cannot Set Property — Getter-Only — What It Means & How to Fix It

What Does This Error Mean?

This error means you tried to assign a value to a property that is read-only — it has a 'getter' but no 'setter'. In JavaScript, you can define object properties that only allow reading (getter) without allowing writing (setter). If you try to assign to such a property, JavaScript throws this TypeError. The fix depends on the object — either use a different method to update it, or find where the property was defined and add a setter.

Affected Models

All browsers
Node.js
All JavaScript environments

Common Causes

Trying to assign to a computed (getter-only) property defined with Object.defineProperty without a setter
Attempting to set a read-only property in a library or framework object
Setting a property on a frozen object (Object.freeze() makes all properties read-only)
Trying to assign to a class property that only has a get accessor and no set accessor
Assigning to a built-in read-only property like window.location.origin or Math.PI

How to Fix It

Check whether the object was frozen with Object.freeze(). If so, properties cannot be set at all. You will need to work with a non-frozen copy.

To create a modifiable copy: const copy = Object.assign({}, frozenObject); — this creates a new object with the same properties that you can modify.
If the property is defined in your own class with only a 'get' accessor, add a 'set' accessor to allow writing.

Example: get name() { return this._name; } set name(value) { this._name = value; } — without the set, trying to assign to .name throws this error.
If the property belongs to a library or framework, use the library's official API to update it instead of direct assignment.

Libraries often protect internal state by making properties read-only, forcing you to use their methods. Read the library documentation for the correct update method.
Check if Object.defineProperty was used to define the property. If 'writable: false' was set or only a get was provided without a set, you cannot assign to it.

To check: Object.getOwnPropertyDescriptor(myObject, 'propertyName') — look for writable: false or the absence of a set function.
If you need to force-write to a property (advanced), use Object.defineProperty with writable: true — but be careful as this can break objects that rely on the property being read-only.

This is a last resort and generally a sign of fighting against the design of the object. Use the intended API instead.

When to Call a Professional

This error requires understanding where the property is defined to fix it properly. Check whether the object is frozen, whether a library is protecting it, or whether a setter needs to be added to a class. For third-party library objects, use the library's official API methods instead of direct property assignment.

Frequently Asked Questions

What is a getter and setter in JavaScript?

A getter is a special function that runs when you read a property — it computes or returns a value. A setter is a special function that runs when you assign a value to a property — it processes the new value. You define them with the 'get' and 'set' keywords inside a class or object. If only a getter is defined, the property is effectively read-only.

What is Object.freeze() and when would it be used?

Object.freeze() makes an object completely immutable — no properties can be added, removed, or changed. It is used when you want to protect a configuration object or a set of constants from being accidentally changed. After freezing, any attempt to modify the object silently fails in non-strict mode, or throws a TypeError in strict mode.

How do I check if a property is read-only?

Use Object.getOwnPropertyDescriptor(obj, 'propName') to inspect a property's attributes. If it shows writable: false, the property cannot be reassigned. If it shows a get function but no set function, it is a getter-only property. If Object.isFrozen(obj) returns true, ALL properties on the object are read-only.