Private setter typescript?

Question

Is there a way to have a private setter for a property in TypeScript?

class Test {     private _prop: string;     public get prop() : string     {         return this._prop;     }      private set prop(val: string)     {         //can put breakpoints here         this._prop = val;     } } 

Compiler complains that visibility for getter and setter don't match. I know I can just set the backing field, but but then I can't set breakpoints when the value is set.

I though about using an interface to hide the setter, but interfaces can only define a property, not whether it has a getter on setter.

Am I missing something here? There doesn't seem to be any reason to not allow private setters, the resulting JS doesn't enforce visibility anyway, and seems better that the current alternatives.

Am I missing something? If not is there a good reason for no private setters?

Answer 1

The TypeScript specification (8.4.3) says...

Accessors for the same member name must specify the same accessibility

So you have to choose a suitable alternative. Here are two options for you:

You can just not have a setter, which means only the Test class is able to set the property. You can place a breakpoint on the line this._prop =....

class Test {     private _prop: string;     public get prop() : string     {         return this._prop;     }      doSomething() {         this._prop = 'I can set it!';     } }  var test = new Test();  test._prop = 'I cannot!'; 

Probably the ideal way to ensure private access results in something akin to a "notify property changed" pattern can be implemented is to have a pair of private get/set property accessors, and a separate public get property accessor.

You still need to be cautious about someone later adding a direct call to the backing field. You could get creative in that area to try and make it less likely.

class Test {     private _nameBackingField: string;      private get _name() : string     {         return this._nameBackingField;     }      private set _name(val: string)     {         this._nameBackingField = val;         // other actions... notify the property has changed etc     }      public get name(): string {         return this._name;     }      doSomething() {         this._name += 'Additional Stuff';     } }