`this`: methods versus functions
Brendan Eich
brendan at mozilla.com
Wed Nov 9 16:23:54 PST 2011
On Nov 9, 2011, at 4:15 PM, Mark S. Miller wrote:
> On Wed, Nov 9, 2011 at 4:00 PM, Brendan Eich <brendan at mozilla.com> wrote:
> On Nov 9, 2011, at 3:48 PM, Axel Rauschmayer wrote:
>
> We talked about lexical this for functions long ago (Jan. 2008? at Google anyway) and IIRC Mark found a subtler flaw.
>
>
> I think my original example was smaller and more elegant.
I remember longer, but could be misremembering. Anyway, your example here is great, thanks!
/be
> But the following is adequate to demonstrate the problem:
>
> function Outer(secret) {
> "use strict";
>
> this.v = secret;
> this.w = secret * 2;
> this.x = secret * 3;
>
> this.InnerPoint = function(x, y) {
> this.x = x;
> this.y = y;
> };
> this.InnerPoint.prototype = {
> getX: function() { return this.x; },
> getY: function() { return this.y; }
> };
> }
>
> Alice does:
> var outer = new Outer(mySecret);
> var innerPoint = new outer.InnerPoint(3,5);
> bob(innerPoint); // passed innerPoint to Bob, who Alice does not trust.
>
> Today, Bob, receiving innerPoint, has no way to obtain Alice's secret. Given your proposal, Bob could do
>
> (1,innerPoint.getX)() / 3;
>
> Today, if Bob does that, the getX call fails when it tries to evaluate undefined.x.
>
> --
> Cheers,
> --MarkM
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