Controlled assignment
Normalize or validate values before storing them.
TypeScript · Const
accessor
TypeScript accessors use get and set methods to control property reads and writes while preserving property-like syntax. A getter-only accessor is inferred as readonly.
How it works
Accessor pairs intercept reads and writes to a class member. A getter supplies the value returned by a read, while a setter receives assigned values and can validate, normalize, or otherwise control the update.
Syntax
class Type {
get property(): ValueType { ... }
set property(value: ValueType) { ... }
}Returns
A getter returns the value read from the member; a setter handles assignment and does not return a member value.
Key points
- Use
getandsetdeclarations to intercept reads and writes to an object member. - Accessors provide finer-grained control over member access, such as validation or normalization during assignment.
- A class can expose property-like access while implementing custom getter and setter behavior.
- Getter-only members communicate their read-only contract in generated declaration files.
Common mistakes
- Accessor syntax requires an ECMAScript 5-or-later output target; ECMAScript 3 output does not support it.
- A getter without a setter is treated as readonly, so callers cannot assign through that property.
Example: Getter and setter accessors
class Person {
private _name: string;
constructor(name: string) {
this._name = name;
}
get name(): string {
return this._name;
}
set name(value: string) {
this._name = value.trim();
}
}
const person = new Person("Ada");
person.name = " Grace ";
console.log(person.name);The getter controls reads and the setter validates or transforms writes to the same property.
When to use it
Computed properties
Expose computed data through property syntax.
Encapsulation
Keep implementation storage private while exposing a stable member API.
Interview questions
QWhat are TypeScript accessors used for?
A getter runs when code reads a member, and a setter runs when code assigns to it. This lets a class control access rather than exposing storage directly.
Follow-up: What happens if only a getter exists? The property is inferred as readonly.
QWhat compiler target constraint applies to accessors?
The compiler must emit ECMAScript 5 or newer for accessors. ECMAScript 3 output is unsupported.
Follow-up: How can a getter-only property communicate its write restriction in generated declarations? It is represented as readonly.
QHow does TypeScript treat a getter with no setter?
A getter without a corresponding setter is automatically inferred as readonly. This also makes the restriction visible to consumers of generated declaration files.
Follow-up: Can a class still update the underlying value internally? Yes, provided the implementation has appropriate private storage or another internal mechanism.
Related
getsetreadonlyClasses