Class Constructor Methods

In every class definition written, there should be at least one method; that is the constructor method. Furthermore, typically this should be the first method defined.

The constructor method is always called by JavaScript when creating a new object from a class. Therefore you must have a constructor method. You can think about it as; “JavaScript must ‘construct’ or build a new object. The constructor method is how a new object gets built.”

The Purpose of the Constructor Method

JavaScript uses the constructor method to build new objects of a class type. Although have not seen how to instantiate a new object from a class yet, you need to accept, that the constructor method is called by JavaScript.

So what goes in a constructor method?

The constructor method should be used to setup or initialize an objects properties.

As an example, if we were creating a digital car, we may want to specify properties such as;

• color
• make
• model
• year

You will learn more specifically how to do this on the next page.

Pseudo Code

As mentioned, the constructor method should be the first method in a class definition.

Furthermore, if there is data that needs to be shared with the newly created object, this should be represented as input parameters to this function.

Roughly, this may look like;

// a class definition
class ClassName {

    // constructor method
    constructor( inputParameter1, inputParameter2 ) {
        // method function block
        // Do stuff here to create an object
        console.log(inputParemeter1);
    }
}