Safari: "TypeError: Attempting to change the setter of an unconfigurable property."

[miztroh-zz]

JS Bin provided below. Confirmed working on Chrome, Firefox, IE11, and Edge. Safari errors out with the message above.

http://jsbin.com/hatuxapodu/edit?html,output

[dfreedm]

Wow, this is actually a Safari bug!

This also shows this issue, only in Safari: http://jsbin.com/miwukeyeto/edit?html,console

[dfreedm]

@kevinpschaaf and I found there are four problems here.

1. the literal 0 in the binding is creating an accessor, element[0].
2. In Safari, a for in loop over an object will repeat numeric keys if that object as a property set with Object.defineProperty
3. The accessors polymer creates for data binding are non-configurable.
4. In Safari, numeric keys will not honor getters and setters on the prototype for numeric keys

var proto = {};
Object.defineProperty(proto, '0', {
  get: function(){},
  set: function(){}
});
var o = Object.create(proto);
o[0] = 3;
// o[0] === undefined in Chrome, Firefox, and IE
// o[0] === 3 in Safari

The end result is that the accessor for the 0 literal is being defined twice on the model in Safari, which throws that the property is non-configurable.

[dfreedm]

Filed issue 4 above as https://bugs.webkit.org/show_bug.cgi?id=151812

[kevinpschaaf]

Root cause issue that results in triggering the Safari bug with reduced repro here: #3128. Will likely just fix that to avoid the Safari bug here to resolve both.

[kevinpschaaf]

Will be fixed in #3153.

JSBin repro using PR branch: http://jsbin.com/zapido/edit?html,output works on Safari now.

[miztroh-zz]

@kevinpschaaf Your JSBin doesn't seem to work on El Capitan / Safari 9.0.2. Enable the console and you should see the same errors I'm getting.

[kevinpschaaf]

Sorry, the branch I pointed to in that bin was merged to master and deleted, so I guess polygit defaults back to the last release when it can't find the branch.

Here's a new jsBin that points to master, showing it fixed: http://jsbin.com/yuturakaxi/1/edit?html,console,output

[miztroh-zz]

@kevinpschaaf Ah, perfect. Any idea when we can expect this commit to make it into a release?

[miztroh-zz]

@azakus Thanks for diagnosing this through the Polymer layer to base issue and reporting the bug to WebKit.

[kevinpschaaf]

@miztroh It's possible we push a release today, if not next week.

[miztroh-zz]

@kevinpschaaf There hasn't been a release since this was fixed in master. I've got several places across a website that are just broken in Safari. Can you give an update as to when we can expect a release?

[kevinpschaaf]

We are doing pre-release tests now with the goal of getting one cut this week.