TypeScript 中的 (this:ClassName) 参数是什么意思？

Question

I am a newbie to TypeScript. I was confused what (this:ClassName) parameter of a function mean in an abstract class. For example:

abstract class Department{
   abstract describe(this:Department):void;
}

class ITDepartment extends Department{
    describe(){
        console.log('IT Department');
    }
}

As above, the implementing child class does not have any parameter for describe() method, but the parent class has the parameter of (this:Department). What is this code telling me and why does this code work??

Answer 1

welcome to SO.

In TypeScript, if you've after a variable or parameter declaration a colon its defining the type of the given variable.
In your case you're declaring the this variable as type Department .
Normally you don't do this with class member functions, because the type of this is already known as the type of the class.