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JavaScript Object-Oriented JavaScript (2015) Constructor Functions and Prototypes Creating Multiple Instances with Constructors

Tony Brackins
Tony Brackins
28,766 Points

Constructor variables

For JS constructor variables. We use something like "this.name = name".

However, we don't have variables named "name". Shouldn't we have to create it first?

1 Answer

Hey Tony, So a constructor function might look like this right?

function myThingy(name, color, type) {
    this.name = name; //line 1
    this.color = color; //line 2
    this.type = type; // line 3
}

Well, this.name would then refer to the current instance of this constructor function.... ya know, whatever new myThingy() might be. When it says = name, it's not creating a new variable though. It's actually just referencing the value of the parameter "name".

In other words, line 1 says that every time you create a new object using this constructor, the first argument supplied to that new object, becomes equal to (becomes the value of) that new object's "name" property. And line 2 says the same thing... except every new object gets a "color" property equal to the 2nd argument supplied. And same with the line 3, with the 3rd argument supplied.

Hope that makes sense. No variables are being declared here.

Tony Brackins
Tony Brackins
28,766 Points

Got it. So it's making the property and not a variable. I'm having a hard time because I'm thinking of constructors in Java and you have to make the variables.

Mmm I feel you. It's weird coming from a classical inheritance language and dealing with JavaScript's prototypal inheritance. You should check this article out here. It does a great job of helping you connect the dots. Kinda of a long read though, but its worth it man.