Constructors in classes in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a constructor in a JavaScript class?

A constructor is a special method in a class that runs automatically when a new object is created. It sets up the object with initial values.

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How do you define a constructor inside a JavaScript class?

You define it using the keyword <code>constructor()</code> inside the class body. It looks like a regular method but named <code>constructor</code>.

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What happens if you don't write a constructor in a JavaScript class?

If no constructor is written, JavaScript uses a default constructor that does nothing but allows object creation.

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Can a JavaScript class have more than one constructor?

No, a class can only have one constructor method. Trying to add more will cause an error.

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How do you use parameters in a constructor?

You add parameters inside the constructor() parentheses and use them to set properties on the new object.

What keyword is used to define a constructor in a JavaScript class?

A create

B init

C build

D constructor

The constructor method is defined using the keyword constructor inside the class.

What happens if you create an object from a class without a constructor?

A JavaScript throws an error

B A default constructor runs

C The object is not created

D You must add a constructor manually

If no constructor is defined, JavaScript uses a default constructor that allows object creation.

How many constructors can a JavaScript class have?

A As many as you want

B Two

C One

D None

A class can only have one constructor method.

Where do you put parameters to initialize object properties in a constructor?

A Inside the constructor parentheses

B After the class keyword

C Inside the class but outside the constructor

D In a separate method

Parameters go inside the constructor parentheses to set initial values.

Which of these is a correct constructor syntax in JavaScript?

A constructor() { this.name = 'John'; }

B function constructor() { this.name = 'John'; }

C class constructor() { this.name = 'John'; }

D new constructor() { this.name = 'John'; }

The constructor is defined as a method inside the class without the function keyword.

Explain what a constructor does in a JavaScript class and why it is useful.

Think about how you prepare a new object with starting values.

Describe how you would add parameters to a constructor and use them to set object properties.

Consider how you pass information when creating a new object.