Access modifiers
All class members are public, by default. This means that they are accessible from outside of the containing class. You saw an example of this earlier when you returned the value of two members of the Car class: _color (a property defined in the class) and color (a parameter defined in the constructor.) Sometimes it is desirable to provide access to both, but you will typically want to control access to the raw data contained in the property by only allowing access through the get or set accessor.
You can also control access to method functions. For example, the Car class contains a function called worker that is only called from other method functions within the class. Calling this function directly from outside of the class may cause undesirable results.
In TypeScript, you can control the visibility of class members by adding the public, private, or protected keyword before the member name.
| Access modifier | Description |
|---|---|
public |
If you don't specify an access modifier, the default is public. You can also explicitly set the member to public by using the public keyword. |
private |
If you modify the member with the private keyword, it cannot be accessed from outside of its containing class. |
protected |
The protected modifier acts much like the private modifier with the exception that members declared protected can also be accessed within deriving classes. (You'll learn more about this later in the module.) |
In addition, properties can be made readonly by using the readonly modifier. Readonly properties may only be set when initialized at their declaration or in the constructor.
Note
TypeScript is a structural type system. When you compare two different types, regardless of where they came from, if the types of all members are compatible, then we say the types themselves are compatible. However, when comparing types that have private and protected members, these types are treated differently. For two types to be considered compatible, if one of them has a private member, then the other must have a private member that originated in the same declaration. The same applies to protected members.