ES6 proxies cannot intercept array indices

Question

Here is my test code (to be run using node --harmony-proxies foo.js:

var a = Proxy.create({
    get : function (proxy, prop)
    {
        return 5
    }
})


console.log(a['foo'])
console.log(a.length)
console.log(a['10'])
console.log(a[10])

Why the last 2 lines fail to print 5, why the proxy fails to intercept properties looking like integers? Is it an implementation bug or is it how it is specified? Is there a separate way to intercept array indices so I can implement my own arrays (e.g. sparse arrays)?

That would be a bug. Which version of node is that, and which version of V8 is it based on? — Andreas Rossberg, May 26 '12 at 07:24
Your example runs well on my NodeJS v0.8.14 installed with NVM. — Tim Wu, Dec 29 '12 at 08:30
Yes it was an issue with proxies not implemented properly in 0.6.x. I voted to close it as it won't probably help future visitors. — nponeccop, Dec 29 '12 at 09:48

score 1 · Accepted Answer · answered May 26 '12 at 20:10

If I read the node changelogs correctly, then node 0.6.18 is still running on V8 3.6.6, which is a fairly old version (from October 2011). In that version, support for proxies was still work in progress (as the other supported Harmony features). Don't expect proxies to function properly before V8 3.8 (from December 2011). Unfortunately, I cannot tell you when the stable version of node will upgrade beyond that.

score 1 · Answer 2 · answered May 27 '12 at 16:32

As A. Rossberg indicated, that bug (and a couple of other showstoppers) are fixed in V8 3.8 (node 0.7.x is quite stable and 0.8.x nears release). If you're working with proxies though, there's still some bugs that you'll have to watch out for. This github issue has a pretty good quick overview of them: https://github.com/tvcutsem/harmony-reflect/issues/4

ES6 proxies cannot intercept array indices

2 Answers2