inheritance - How to create Abstract base class in JavaScript that can't be Instantiated

Question

I have a class

function Node() {
    //implementation
}

and another class

function AttributionalNode() {
    this.prototype.setAttr = function (attr) {
        this.atText = attr;
    };
}

AttributionalNode.prototype = new Node();
AttributionalNode.prototype.constructor = AttributionalNode;

How to make class Node() so it can't be instantiated? e.g when I try

var node = new Node();

So it throws an Exception?

Answer 1

In JavaScript engines that support ECMAScript 2015 (aka ES6) class syntax, this can be accomplished using the new.target meta-property:

function Node() {
   if (new.target === Node) throw TypeError("new of abstract class Node");
}

or using class syntax:

class Node {
   constructor () {
      if (new.target === Node) throw TypeError("new of abstract class Node");
   }
}

in either case, just define AttributionalNode as:

class AttributionalNode extends Node {
   constructor () {
      super();
   }
   setAttr(attr) {
      this.atText = attr;
   }
}

new Node();               // will throw TypeError
new AttributionalNode();  // works fine

For a more detailed explanation of new.target see section 4.2 of this document.