Private setter typescript?

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';
    }
}