Mastering TypeScript 3 - Third Edition

strictPropertyInitialization

Similar to the strictNullChecks compile option, we can also check whether the properties of a class have been initialized correctly using the strictPropertyInitialization compiler flag. Consider the following class definition:

class WithoutInit { 
    a: number; 
    b: string; 
} 

Here, we have a standard class definition for a class named WithoutInit. This class has two properties, named a, of type number, and b, of type string. With the strictPropertyInitialization compile option turned on, this code will generate the following errors:

error TS2564: Property 'a' has no initializer and is not definitely assigned in the constructor.
error TS2564: Property 'b' has no initializer and is not definitely assigned in the constructor. ...