This error occurs when you try to use getter or setter syntax in a context where TypeScript does not allow it, such as in object literals, declaration files, or with invalid syntax patterns. Accessors have strict placement rules in TypeScript and can only be defined in class bodies or certain interface contexts. Understanding where accessors are valid prevents syntax errors and ensures proper encapsulation.
TypeScript accessors (getters and setters) are special class members that allow you to intercept property access and modifications. However, they can only be used in specific contexts: class bodies and certain TypeScript-specific declarations. When you try to define an accessor in an invalid location—such as inside an object literal, in a function, at the module level, or in a declaration file without proper context—TypeScript raises this error. The error message indicates that the accessor syntax (get/set keywords) has been used in a place where TypeScript does not expect or allow it. This is fundamentally a structural issue with where you have placed your code, not a logic error.
Look at the error message in your TypeScript compiler output or IDE. It will point to the exact line where the accessor is defined. Note whether you are using get or set keyword and what context it appears in (inside braces, at module level, etc.).
Accessors are only valid in class definitions. If you have a getter or setter in an object literal or at module level, you must wrap it in a class.
// WRONG - accessor in object literal
const user = {
_age: 25,
get age() { // Error: Accessor is not valid here
return this._age;
}
};
// CORRECT - accessor in class
class User {
private _age = 25;
get age() {
return this._age;
}
}
const user = new User();
console.log(user.age); // 25If you only need a getter without the encapsulation benefits of a class, you can use a regular function property or a method instead of an accessor.
// Alternative: use a method instead of getter
const user = {
_age: 25,
getAge() { // Use a method instead
return this._age;
},
setAge(age: number) { // Separate setter method
this._age = age;
}
};
console.log(user.getAge()); // 25
user.setAge(30);Ensure your accessor follows the correct TypeScript syntax. The get or set keyword must directly precede a method name (not a function keyword).
// WRONG - using function keyword with accessor
class User {
get function age() { // Error: invalid syntax
return this._age;
}
}
// CORRECT - no function keyword
class User {
get age() { // Correct accessor syntax
return this._age;
}
}In declaration files (*.d.ts), accessors must be inside a class or type definition. You cannot declare accessors at the module level in declaration files.
// user.d.ts - WRONG
get age(): number; // Error: Accessor is not valid here
// user.d.ts - CORRECT
declare class User {
get age(): number;
}If you need a property that cannot be modified after initialization, you can use readonly instead of creating a getter.
class User {
readonly age: number; // Simple and clean
constructor(age: number) {
this.age = age;
}
}
// Or with a getter for computed values
class User {
private _birthYear: number;
get age(): number { // Computed from birthYear
return new Date().getFullYear() - this._birthYear;
}
}Accessors in TypeScript are syntactic sugar that compile to getter and setter functions in the emitted JavaScript. They are strictly class-level members and cannot be used in other contexts because JavaScript itself only supports accessors on object literals and class bodies, not at module level. If you are working with third-party types that seem to use accessor syntax in unexpected places, you may be looking at a type definition issue; check the declaration file to understand the intended structure. In some cases, you might want to use a factory function that returns an object with a proxy to intercept property access, but this is more complex than using a simple class. Remember that accessors are only available when targeting ES5 or higher in your TypeScript configuration; if you target ES3 or ES4, you cannot use accessors at all.
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