InstanceType type in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the InstanceType type do in TypeScript?

<p><code>InstanceType</code> takes a class type and returns the type of instances created by that class.</p>

beginner

How do you use <code>InstanceType</code> with a class named <code>Car</code>?

You write InstanceType<typeof Car> to get the type of an object created by new Car().

beginner

Can InstanceType be used with interfaces or only classes?

<p><code>InstanceType</code> works only with class constructors, not interfaces.</p>

intermediate

What happens if you use InstanceType on a type that is not a constructor?

TypeScript will give an error because InstanceType expects a constructor type.

beginner

Why is InstanceType useful in TypeScript?

<p>It helps you get the instance type from a class type, so you can write safer and clearer code without repeating types.</p>

What does InstanceType return?

A The type of instances created by MyClass

B The type of the MyClass constructor function

C The static properties of MyClass

D The interface implemented by MyClass

InstanceType extracts the instance type from a class constructor type.

Can InstanceType be used with a function type?

A Yes, always

B Yes, but only with arrow functions

C No, only with class constructors

D Only if the function returns an object

InstanceType requires a class constructor type, not a regular function type.

What keyword do you use inside InstanceType to refer to a class type?

A new

B typeof

C instanceof

D class

You use typeof to get the type of the class constructor.

If you have class Dog { bark() {} }, what type does InstanceType have?

A An object with a <code>bark</code> method

B The Dog class itself

C A function type

D Undefined

The instance type includes the bark method defined in the class.

What error occurs if you use InstanceType on a non-constructor type?

A Syntax error

B No error, it works fine

C Runtime error

D TypeScript error: Type is not a constructor

TypeScript expects a constructor type and will error if given something else.

Explain how InstanceType helps when working with classes in TypeScript.

Think about how you get the type of an object created by a class.

Describe a situation where using InstanceType would prevent a type error in your code.

Consider when you want to refer to the type of an object created by a class without writing it yourself.