What structural typing means in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is structural typing in TypeScript?

Structural typing means that TypeScript checks if two types are compatible based on their shape or structure, not their names. If the properties and types match, they are considered compatible.

intermediate

How does structural typing differ from nominal typing?

Structural typing compares the actual content (properties and methods) of types, while nominal typing compares types by their names or explicit declarations.

beginner

Example: Are these two types compatible in TypeScript?<br>

type A = { name: string };
type B = { name: string; age: number };

No, type A is not assignable to type B because it lacks the 'age' property. However, type B is assignable to type A because it has all required properties of A plus extra ones, which are allowed in structural typing.

beginner

Why is structural typing useful in TypeScript?

It allows flexible and easy code reuse by focusing on what data looks like rather than what it is called. This helps when working with different objects that share the same shape.

intermediate

Can two different classes be compatible in TypeScript under structural typing?

Yes, if their public properties and methods match in shape, TypeScript considers them compatible even if they come from different classes.

What does structural typing check in TypeScript?

A The names of types

B The shape or structure of types

C The file location of types

D The order of declaration

Structural typing compares the properties and their types, not the names or locations.

If two objects have the same properties and types, TypeScript considers them:

A Incompatible

B Only compatible if declared with the same name

C Only compatible if from the same class

D Compatible

TypeScript uses structural typing, so matching shapes mean compatibility.

Which typing system compares types by their names rather than structure?

A Structural typing

B Duck typing

C Nominal typing

D Dynamic typing

Nominal typing checks type names explicitly.

In TypeScript, can an object with extra properties be assigned to a type with fewer properties?

A Yes, if the required properties match

B No, extra properties cause errors

C Only if explicitly cast

D Only if using interfaces

Extra properties are allowed if the required ones match the target type.

Structural typing helps TypeScript by:

A Focusing on data shape for compatibility

B Making code less flexible

C Requiring explicit type names

D Preventing object reuse

Structural typing focuses on the shape of data to allow flexible compatibility.

Explain in your own words what structural typing means in TypeScript and why it matters.

Think about how two objects with the same properties can be used interchangeably.

Describe a real-life example where structural typing helps when working with different objects.

Imagine two different forms that have the same fields.