Constructor functions in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a constructor function in JavaScript?

A constructor function is a special function used to create and initialize objects. It sets up properties and values for new objects using the new keyword.

beginner

How do you call a constructor function to create a new object?

You call a constructor function with the <code>new</code> keyword before the function name, like <code>const obj = new MyConstructor();</code>. This creates a new object and runs the constructor code.

beginner

What does the this keyword refer to inside a constructor function?

Inside a constructor function, this refers to the new object being created. You use this to add properties or methods to that new object.

intermediate

What happens if you forget to use new when calling a constructor function?

If you forget new, the constructor function runs like a normal function. this will not point to a new object, which can cause errors or unexpected results.

intermediate

How can you add methods to all objects created by a constructor function?

You add methods to the constructor's prototype. For example, MyConstructor.prototype.sayHi = function() { console.log('Hi'); };. All objects created will share this method.

What keyword do you use to create a new object with a constructor function?

A new

B create

C object

D construct

The new keyword creates a new object and runs the constructor function.

Inside a constructor function, what does this refer to?

A The constructor function itself

B The global object

C The new object being created

D Undefined

this points to the new object created by the constructor.

What happens if you call a constructor function without new?

A It returns null

B It throws a syntax error

C It creates a new object anyway

D It runs as a normal function, <code>this</code> is not the new object

Without new, the function runs normally and this does not refer to a new object.

How do you add a method shared by all objects created by a constructor?

A Add it to the constructor's prototype

B Use a global variable

C Add it to each object manually

D Add it inside the constructor function

Adding methods to the constructor's prototype shares them across all created objects.

Which of these is a correct constructor function name by convention?

A person

B Person

C personConstructor

D createPerson

Constructor functions usually start with a capital letter to distinguish them.

Explain how a constructor function works in JavaScript and how you create an object with it.

Think about how you make a new object and set its properties.

Describe how to add a method that all objects created by a constructor function can use.

Where do you put methods so all objects share them?