CODEWITHSUNDEEP
javascriptsyntaxecmascript-6
Daniel Mizerski
Daniel Mizerski

Reputation: 1131

ES6 js "with" keyword

In the deep internet I encountered structure like class A extends B with C { ... }, I haven't link right now, it was like macro for class while extending abstract class.

Is this in standard? (I googled, only finding old with that is removed right now, chrome inline console throws error)

Upvotes: 4

Views: 612

Answers (2)

Oriol
Oriol

Reputation: 288100

It's not standard. From Annex A.4 - Functions and Classes, the syntax is

ClassDeclaration[Yield, Default] :
    class BindingIdentifier[?Yield] ClassTail[?Yield]
    [+Default] class ClassTail[?Yield]

ClassExpression[Yield] :
    class BindingIdentifier[?Yield]opt ClassTail[?Yield]

ClassTail[Yield] :
    ClassHeritage[?Yield]opt { ClassBody[?Yield]opt }

ClassHeritage[Yield] :
    extends LeftHandSideExpression[?Yield]

So the ClassTail is the part which includes both the optional extends something and the class body. And that something must be a LeftHandSideExpression, without any with in there.

Upvotes: 2

Red Mercury
Red Mercury

Reputation: 4310

No this is not a part of the ECMAScript 6 Classes standard. See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes

The with keyword is used in some programming languages to signify multiple inheritance.

Scala for example has traits which classes can extend from with the with keyword

trait Drawable {
    def draw() { }
}

trait Cowboy extends Drawable {
    override def draw() { println("Bang!") }
}

trait Artist extends Drawable {
    override def draw() { println("A pretty painting") }
}


class CowboyArtist extends Cowboy with Artist

Upvotes: 2

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