Super keyword behavior in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the super keyword do in TypeScript classes?

The super keyword is used to call functions on an object's parent class. It allows access to the parent class's constructor and methods.

beginner

When must you call <code>super()</code> in a derived class constructor?

You must call <code>super()</code> before using <code>this</code> in a derived class constructor. This ensures the parent class is properly initialized first.

intermediate

How do you use <code>super</code> to call a parent class method that is overridden?

Inside the child class method, use <code>super.methodName()</code> to call the parent class's version of the method.

intermediate

Can <code>super</code> be used outside of class methods or constructors?

No, <code>super</code> can only be used inside class constructors or methods to refer to the parent class. Using it outside causes errors.

beginner

What happens if you forget to call <code>super()</code> in a derived class constructor?

TypeScript will throw an error because the parent class constructor must be called before accessing <code>this</code>. This prevents incomplete initialization.

What is the purpose of the super() call in a derived class constructor?

A To override a method

B To create a new instance of the child class

C To call a static method

D To initialize the parent class before using <code>this</code>

The super() call initializes the parent class, which must happen before using this in the derived class constructor.

How do you call a parent class method named greet from a child class?

A <code>super.greet()</code>

B <code>this.greet()</code>

C <code>parent.greet()</code>

D <code>greet.super()</code>

Use super.greet() inside the child class method to call the parent class's greet method.

Can you use super outside of a class method or constructor?

A Yes, anywhere in the code

B No, only inside class methods or constructors

C Only inside static methods

D Only inside arrow functions

super is only valid inside class constructors or methods to access the parent class.

What error occurs if you use this before super() in a derived class constructor?

A ReferenceError

B SyntaxError

C TypeError

D No error

Using this before calling super() causes a ReferenceError because the parent class is not initialized yet.

Which statement about super is true?

A <code>super</code> is a variable holding the parent class

B <code>super</code> creates a new instance of the parent class

C <code>super</code> can be used to access parent class properties and methods

D <code>super</code> can be used in any function

super is used to access the parent class's properties and methods from a child class.

Explain how and why you use the super keyword in a TypeScript class constructor.

Think about what happens when you create a child class object.

Describe how to call a parent class method from a child class when the method is overridden.

How do you reach back to the original method?