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JavaScript

Jannick Moth
Jannick Moth
8,714 Points
Posted by Jannick Moth
Jannick Moth
8,714 Points

How is owner.id working?

I'm not sure how owner.id is declaring itself. I tested the code and I see that it creates a unique value but I can't work out how it gets there

class Token { constructor(index, owner){ this.owner = owner; this.id = token-${index}-${owner.id}; this.dropped = false; } }

class Player { constructor(name, id, color, active = false) { this.name = name; this.id = id; this.color = color; this.active = active; this.tokens = this.createTokens(21); }

createTokens(num) {
    var array = [];
    for(var i = 0; i < num; i ++) {
        var newCounter = new Token(i, this);
        array.push(newCounter);
    }
    return array;
}

}

Any explanations?

Thanks in advance.

2 Answers

Steven Parker
Steven Parker
231,172 Points
Steven Parker
Steven Parker
231,172 Points

We can see from this code that any object of class "Player" is passed an id (along with a name and color) when it is constructed. Then, when an item of type "Token" is created, an index number and a reference to a "Player" object is passed in.

The unique ID established in a "Token" object comes from this assigment:

this.id = `token-${index}-${owner.id}`;

That's a template string. Each identifier along with the braces and leading dollar sign will be replaced by the string representation of the value that the identifier contains. This process is called interpolation.

For example, if the variable "index" contains 3, and the "owner" has an "id" set to "joe", then `token-${index}-${owner.id}` would be interpolated into the string "token-3-joe".

Steven Parker
Steven Parker
231,172 Points
Steven Parker
Steven Parker
231,172 Points

In answer to your additional questions: Yes, if a property is also an object it can certainly have properties of its own.

A more granular breakdown of the "owner.id" reference:

  • when a "Player" object is created, its constructor is given an "id" as an argument
  • when a "Token" is created, its constructor is given an "index" and an "owner" (which is a "Player" object)
  • the "index" and the "id" of the "owner" are both combined in a template string to create the Token's "id"

If it's still not clear it might help to look at some of the code where these definitions are actually used.

Jannick Moth
Jannick Moth
8,714 Points
Jannick Moth
Jannick Moth
8,714 Points

Hi Steven, thanks for the reply

I think I understand the template literal part, but I'm still confused as to when owner.id is declared. As I understand it, it's only mentioned once (in the template literal) - and owner is never declared as an object, only as the property of an object.

How does the player.id property find it's way to the owner.id property? Can a property have properties of it's own? is "id" a variable that is passed in and then any time it's mentioned in the objects it is called to that value?

Thanks again, Jannick