Thank you for the detailed explanation. Now I have a better understand of the
export declaration.
> I would have no idea what `export default var a = 1;` was supposed to mean.
Looking back, this does seem unclear, but indulge me to share how I come up
with the proposed syntax:
I was trying to export a point data structure for the mouse position. This was
my initial try:
export var x = 0;
export var y = 0;
document.addEventListener(“mousemove”, (ev) => {clientX: x, clientY: y} = ev);
But then I realized in order to consume it, i need to do “import * as
mousePosition from …”. This doesn’t look right to me, because the exported obj
isn't an aggregation of independent things (the "* as …" syntax looks like a
reminder that properties are independent), I want to use it like “import
mousePosition from …”.
So giving the experience of you can merge export and a variable declaration
into a single line, I tried to do:
export default var pt = { x: 0, y: 0 };
document.addEventListener(“mousemove”, (ev) => {clientX: pt.x, clientY: pt.y} =
ev);
// hope i got the destructuring assignment right
Thus this proposal.
So obviously “merging” concept doesn’t apply when default is involved, and I
now know why. Thanks again.
> On Dec 15, 2014, at 11:31 PM, Dave Herman <[email protected]> wrote:
>
> On Fri, Dec 12, 2014 at 8:19 PM, Glen Huang <[email protected]
> <mailto:[email protected]>> wrote:
> You can already do "var a = 1;export default a;”. Why not make "export
> default var a = 1;” valid?
>
> Because the former is creating an exported variable called 'default' and
> assigning its initial value to the result of evaluating an expression that
> happens to evaluate the current value of 'a'. There's nothing special about
> the fact that you used 'a' there, it's just an ordinary expression that
> happens to evaluate a variable.
>
> (For historical interest, this was why I was in favor of using the equals
> sign in the syntax, to make it clear that export default is doing an
> assignment of an initializer expression to a variable, e.g.:
>
> export default = a;
>
> But this was unpopular and I didn't push the issue.)
>
> At a more basic level, from a "principle of least surprise" perspective, I
> would have no idea what `export default var a = 1;` was supposed to mean.
>
> Dave
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