A new ES6 draft is available

Allen Wirfs-Brock allen at wirfs-brock.com
Sat Jan 17 09:30:58 PST 2015

On Jan 17, 2015, at 5:59 AM, Frankie Bagnardi wrote:

> I'm also expecting a lot of questions about 'what is this new.target thing in this code?', 'is new a variable?', 'where does it come from?', 'isn't new an operator?', etc.

as proposed,
`new.target` is a MemberExpression consisting of  the three token sequence `new`  `.`  `target`
If is only allowed in function code.
If the enclosing function is invoked as a call expression the value of  `new.target` is null
   `(function() {assert(new.target===null)})()
if the enclosing function is directly invoked as a constructor via `new` the value of `new.target` is the function 
    function f() {assert(new.target===f)}
    new f();
if the enclosing function is indirectly invoked as a constructor via `super()` or `new super()` the value of `new.target` is  the function new was directly applied to
    class Super  { constructor() {assert(new.target===Sub)}}
    class Sub extends Super {constructor() {super()}}
    new Sub();

> if (this instanceof MyDate) ...
> ... is clearer, but I guess it needs to be disallowed because of the other rules.

When a function is called (rather than new'ed) its this value is usually undefined (assuming a strict function)


> On Fri, Jan 16, 2015 at 1:29 PM, Brendan Eich <brendan at mozilla.org> wrote:
> Gotta agree new.target is nicer to read and write!
> /be
> Allen Wirfs-Brock wrote:
> err,
>          try {
>               let thisValue = this;  //can't reference 'this' prior to 'super()' in a [[Construct]] call of a derived function
>          } catch (e} {
>             calledAsFunction = false  //no let here
>         }
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