如何在Typescript中定义对象变量的类型？

Question

I have this object variable in the class a :

class a {
  abc = {
    def: number = 22  // won't work
  }
  ghi: number = 23; // works

..

How can I define (inline without using an interface) the type of the variable def that is inside the object abc ?

I tried using this syntax but it will not accept it.

Answer 1

The way it could be - is to use assert and inlined declaration:

class MyClass {
  abc = <{ def : number }>{
    def: 1,
  };  
}

The same, but a bit more readable with explicit interface

interface IMyObject{
  def : number 
}

class MyClass1 {
  abc = <IMyObject>{
    def: 1,
  };  
}

Check it here

And why this?

class a {
  abc = {
    def: number = 22  // won't work
  }
  ghi: number = 23; // works

because the ghi is the member/property of class a - so it is just like this:

class MyClass {
  // standard way how to define properties/members of a class
  public obj: number;
  private other: string;
}

Answer 2

Just FYI. Without using a type assertion:

class a {
  abc : {def:number} = {
    def : 22  // Works
  }
  ghi: number = 23; // works
}

Note: in your case its best to let the compiler infer the type signature for you.