Type compatibility with classes in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does type compatibility mean in TypeScript classes?

It means one class type can be used where another is expected if their structures match, even if they are different classes.

beginner

How does TypeScript check compatibility between two classes?

TypeScript compares the properties and methods of the classes. If one class has at least the same members with compatible types, it is compatible.

intermediate

Can private or protected members affect class compatibility in TypeScript?

Yes. If classes have private or protected members, they must come from the same declaration to be compatible.

beginner

Given two classes with the same public properties, are they compatible?

Yes. If their public properties and methods match in type, they are compatible regardless of class names.

intermediate

Why does TypeScript use structural typing for classes instead of nominal typing?

Because it focuses on the shape of data (members) rather than the class name, making code more flexible and reusable.

In TypeScript, when are two classes considered compatible?

A When their public members have matching types

B Only if they have the same class name

C If they are declared in the same file

D When they have the same number of methods

TypeScript checks if the public members match in type, not the class name or file location.

What happens if two classes have private members with different declarations?

A Private members are ignored in compatibility

B They are always compatible

C They are incompatible

D They become compatible if public members match

Private members must come from the same declaration to be compatible.

Which typing system does TypeScript use for class compatibility?

A Nominal typing

B Structural typing

C Duck typing

D Dynamic typing

TypeScript uses structural typing, meaning compatibility depends on member structure.

If class A has extra public members not in class B, can A be assigned to B?

A Yes, if B's members are present in A

B No, extra members prevent compatibility

C Only if classes share the same name

D Only if extra members are private

Extra members do not prevent compatibility as long as required members match.

Why might TypeScript's class compatibility be helpful in real projects?

A It forces strict class inheritance

B It disables private members

C It requires all classes to have unique names

D It allows flexible use of objects with similar shapes

Structural typing lets you use different classes interchangeably if their shapes match.

Explain how TypeScript determines if two classes are compatible.

Think about comparing the shape of the classes, not their names.

Describe a situation where two classes with the same public properties are not compatible.

Consider private members and their declarations.