allenwb

//The following is essentially the current ES6 spec. for Boolean, expressed in ES code
//$$foo calls are performing spec. level operations that don't have direct ES language equivalents
class Boolean {
  static [Symbol.create](.){
    //@@create allocates the object with private slots but doesn't do any slot initialization
    return $$OrdinaryDateFromConstructor(this,"%BooleanPrototype%",["[[BooleanData]]"]);
    // a newly created Boolean instance has undefined as the value of its [[BooleanData]] internal slot.
    // the undefined value indicates that the instance has not yet been initialized by the constructor function
  }

allenwb

function *enumerate(obj) { 
  if (Object(obj)!==obj) return  undefined;
  let visited = new Set;  
  while (obj!==null ) {
    for (name of Object.getOwnPropertyNames(obj)) { 
      if (!visited.has(name)) {
        let desc = Object.getOwnPropertyDescriptor(obj,name);
        if (desc) {
          visited.add(name);
          if (desc.enumerable) yield name;

allenwb

New ES6 Constructor Semantics and Usage Examples

Auto super: Alternative Design where subclass constructors automatically call their superclass constructors

This Gist presents a new design of class-based object construction in ES6 that does not require use of the two-phase @@create protocol.

One of the characteristics of this proposal is that subclasses constructors automatically super invoke their superclass constructor's object allocation and initialization logic unless the derived constructor expliictly assigns to this.

An alternative version of this proposal eliminates from the design most implicit/automatic invocations of superclass constructors.

In addition to the material below, there is a seperate design rationale covering several key features that are common to both designs.

allenwb

At the July 2014 TC39 meeting, we presented a sketch of a new object instantiation design that was inspired from posting of Claude Pache. Here's the basic idea, as originally described by Claude:

If a constructor C uses super in its code, let’s say:

  class C extends B {
      constructor(...args) {
          /* 1: preliminary code that doesn't contain calls to a super-method */
          // ...

          /* 2: call to a super-constructor */

allenwb

//work in progress

// A response to jashkenas's fine proposal for minimalist JavaScript classes.
// and BrendanEich's Rich Corinthian Leather alternative proposal

//intro and justifications still to come

// Harmony always stipulated classes as sugar, so indeed we are keeping current
// JavaScript prototype semantics, and classes would only add a syntactic form
// that can desugar to ES5. This is mostly the same assumption that Jeremy

allenwb

This is a response to Git 1850768 For some reason the following wouldn't post as a comment

@mranney @piscisaureus

I did some experiments and I don't see any round-tripping issues showing up, at least in FF:

var z= "\ud83d\ude38";   //u+1f638
console.log("z.length: " + z.length); //expect 2

allenwb

Number.prototype.introspect = function() {
    "use strict";  //.See ES5.1 10.4.3 steps 1-3
    if (typeof this == "object") return Object.prototype.introspect.call(this);//generic object mirror
    return new Float(+this); //Number value mirror
};

allenwb

// 1. No new  syntax for non-TCP functions.
//
// This approach does do include a shorter syntax for regular functions, so if a classic JS function
// is what you want you use the classic long form function expression:

a.some(function (x){
    if (invalid(x))
        return true;
    console.log(x);
});

allenwb

####Why is .constructor not good enough? What does doing .constructor[@@species] add?

@@species is an extension point that allows abstract algorithms that may be inherited by (or applied to) various subclasses with differing characteristics to decouple the class of the objects generated by an application of the method from the actual class of the objects the method was applied to. This is a realivately rare situation, but one that does infact occur when developing relatively complex class hierarchies such as a collections hierarchy.

The first known usage of the species pattern that I’m aware of (and the origin of the name species) was in the Smalltalk-80 collection hierarchy. For example, the Smalltalk-80 collection hierarchy includes a class called SortedCollection. SortedCollection is a subclass of OrderedCollection (essentially a double ended queue, similar to a JS Array) except that whenever a new element is added to the collection, the value ordering of the collection is resorted. The familiar operat

allenwb

Object.isAncestorOf = function isAncestorOf(parent,child) {
   if (child===null || child===undefined) return false;
   if (parent === null) return true;
   child = Object(child);
   var proto = Object.getPrototypeOf(child);
   if (proto === parent) return true;
   return isAncestorOf(parent,proto);
}