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
```js
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
```js
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)
Allen
>
> On Fri, Jan 16, 2015 at 1:29 PM, Brendan Eich <[email protected]> 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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