PathObserver doesn't support String keys in index expressions

[jolleekin]

Since observe-dart follows observe-js, I think it is necessary for the team to be aware of the following bug in the Dart implementation.

https://code.google.com/p/dart/issues/detail?id=20294

[jmesserly]

edited subject. Based on your link, I think the issue is property paths like obj["+foo"] don't currently work.

[jolleekin]

No, obj["+foo"] works perfectly. What doesn't work is obj["foo"] and obj[1] if obj is a Map

Why `obj["+foo"] works

obj["+foo"] is correctly parsed into [#obj, "+foo"]

Why obj["foo"] doesn't work

obj["foo"] is parsed into [#obj, #foo] instead of [#obj, "foo"], and #foo may not exist in generated code

Why obj[1] doesn't work if obj is a Map

_getObjectProperty and _setObjectProperty only handle List indexers and ignore Map integer indexers.

_getObjectProperty(object, property) {
  if (object == null) return null;

  if (property is int) {
    if (object is List && property >= 0 && property < object.length) {
      return object[property];
    }
  } else if (property is String) {
    return object[property];
  } else if (property is Symbol) {
  ...
}

bool _setObjectProperty(object, property, value) {
  if (object == null) return false;

  if (property is int) {
    if (object is List && property >= 0 && property < object.length) {
      object[property] = value;
      return true;
    }
  } else if (property is Symbol) {
  ...
}

This problem results from a difference between JS and Dart. In JS, obj.foo and obj["foo"] are identical while, in Dart, they are two completely different things. So not everything that works in JS can work in Dart.

To fix this problem, the parser should reserve indexers (whether they are Map indexers or List indexers) instead of trying to convert them into symbols.

• identifiers => symbols
• string indexers => strings
• int indexers => int's

[jmesserly]

@jolleekin I think you're talking about Dart-specific issues. Those are tracked at https://code.google.com/p/dart/issues/detail?id=20294

[jmesserly]

(This issue tracker is only for issues related to the JavaScript implementation)

[jolleekin]

I know. The problem is observe-dart is implemented based on observe-js. If something doesn't work in the Dart implementation, it must be reflected back to the JS implementation. That's why I opened this issue.

Sent from my Windows Phone

---

From: John Messerlymailto:notifications@github.com
Sent: ‎8/‎12/‎2014 1:46 AM
To: Polymer/observe-jsmailto:observe-js@noreply.github.com
Cc: Man Hoangmailto:jolleekin@outlook.com
Subject: Re: [observe-js] PathObserver doesn't support String keys in index expressions (#64)

(This issue tracker is only for issues related to the JavaScript implementation)

---

Reply to this email directly or view it on GitHub:
#64 (comment)

[jmesserly]

Ah, gotcha. But I wouldn't say it so strongly. There can be differences, if it makes sense. For example, in the case of Map, it's a Dart type and doesn't need (and couldn't) be handled in JavaScript. Same thing with Symbol vs String. That should be addressed in the Dart code (https://code.google.com/p/dart/issues/detail?id=20294). That's why for this bug, we focus only on problems that can be recreated in JavaScript.

[jolleekin]

Maybe I took sigmund's words too serious ("that is also how the JS implementation is written. We have to follow up with them to make sure we are consistent."). Anyway, if the Dart team agrees there can be differences, this issue can be closed.

[rafaelw]

Ok. I'm closing this. If someone feels there is an actual bug in the JS impl, please post a jsbin with expected/actual behavior.