Declaring functions and classes in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

How do you declare a simple function in TypeScript that adds two numbers?

You declare it using the <code>function</code> keyword, specify parameter types, and return type. Example:<br><pre>function add(a: number, b: number): number {<br>  return a + b;<br>}</pre>

beginner

What is the syntax to declare a class with a constructor in TypeScript?

Use the <code>class</code> keyword, define a <code>constructor</code> method to initialize properties. Example:<br><pre>class Person {<br>  name: string;<br>  constructor(name: string) {<br>    this.name = name;<br>  }<br>}</pre>

beginner

What does the <code>this</code> keyword refer to inside a class method?

this refers to the current instance of the class, allowing access to its properties and other methods.

intermediate

How do you declare a function expression with a type annotation in TypeScript?

You can assign a function to a variable with a type. Example:<br><pre>const multiply: (x: number, y: number) => number = (x, y) => x * y;</pre>

intermediate

What is the difference between a function declaration and a function expression in TypeScript?

A function declaration is hoisted and can be called before it is defined. A function expression is assigned to a variable and is not hoisted, so it must be defined before use.

Which keyword is used to declare a class in TypeScript?

A class

B function

C object

D struct

The class keyword is used to declare classes in TypeScript.

What is the correct way to specify the return type of a function that returns a string?

A function greet(): String {}

B function greet(): string {}

C function greet(): str {}

D function greet() -> string {}

In TypeScript, the return type is specified after the parameter list with a colon, like (): string.

How do you access a property named age inside a class method?

A this.age

B self.age

C age

D class.age

Inside a class method, use this.propertyName to access properties.

Which of the following is a valid function expression in TypeScript?

A let f = (x) => x * 2;

B function f(x: number): number { return x * 2; };

C const f = function(x: number): number { return x * 2; };

D var f: function = (x) => x * 2;

Option C shows a valid function expression with type annotations.

What happens if you call a function expression before it is defined?

A It works fine because all functions are hoisted.

B It calls the function but with default parameters.

C It returns undefined.

D It causes an error because function expressions are not hoisted.

Function expressions are not hoisted, so calling them before definition causes an error.

Explain how to declare a class with a constructor and a method in TypeScript.

Think about how you create a blueprint for objects with properties and actions.

Describe the difference between function declarations and function expressions in TypeScript.

Consider when you can call the function in your code relative to where it is written.