What is equivalent to protected in TypeScript?

Question

What is equivalent protected in TypeScript ?

I need to add some member variables to a base class that will only be used in derived classes .

Answer 1

Updates

November 12, 2014. Version 1.3 of TypeScript is available and includes a secure keyword.

September 26, 2014. The protected keyword has landed. This is currently a preliminary release. If you are using a very new version of TypeScript, now you can use the protected keyword ... the answer below is for older versions of TypeScript. Enjoy it.

View Release Notes for a Secure Keyword

 class A { protected x: string = 'a'; } class B extends A { method() { return this.x; } } 

Old answer

TypeScript has only private - it is not protected, and this means only confidentiality during compile time checking.

If you want to access super.property , it must be publicly available.

 class A { // Setting this to private will cause class B to have a compile error public x: string = 'a'; } class B extends A { method() { return super.x; } } 

Answer 2

How about the following approach:

 interface MyType { doit(): number; } class A implements MyType { public num: number; doit() { return this.num; } } class B extends A { constructor(private times: number) { super(); } doit() { return super.num * this.times; } } 

Since the num variable is defined as public, this will work:

 var b = new B(4); b.num; 

But since it is not defined in the interface, it is:

 var b: MyType = new B(4); b.num; 

will result in The property 'num' does not exist on value of type 'MyType' .
You can try this in the playground .

You can also wrap it in a module when exporting only the interface, and then from other exported methods you can return instances (factory), so the total amount of variables will be “contained” in the module.

 module MyModule { export interface MyType { doit(): number; } class A implements MyType { public num: number; doit() { return this.num; } } class B extends A { constructor(private times: number) { super(); } doit() { return super.num * this.times; } } export function factory(value?: number): MyType { return value != null ? new B(value) : new A(); } } var b: MyModule.MyType = MyModule.factory(4); b.num; /// The property 'num' does not exist on value of type 'MyType' 

A modified version in this playground .

I know that this is not quite what you requested, but it is pretty close.

Answer 3

at least at the moment (version 0.9) protected, not specified in specifications

http://www.typescriptlang.org/Content/TypeScript%20Language%20Specification.pdf