<textarea> welcomes user with 'undefined' text value (only for object subproperties)

[slawomir-brzezinski-at-interxion]

Description

An undefined value, when binding to <textarea>, is treated as 'undefined' text, but only if it appears in an object subproperty.
Interestingly null gets treated just fine. undefined in a flat property is also just fine.
<input type="text"> doesn't have the issue.
See the live demo.

Live Demo

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

Expected Results

It should work like <input type="text">

Actual Results

The user value is an 'undefined' text.

Browsers Affected

• Chrome
• Firefox
• Edge
• Safari 9
• Safari 8
• IE 11

Versions

• Polymer: v1.9.1, v2.0.0 (we are using 1.9.1 - please do try to fix 1.X)
• webcomponents: 0.7.24

[TimvdLippe]

For native HTML elements, you should use value$ for bindings instead of value: https://www.polymer-project.org/2.0/docs/devguide/data-binding#anatomy-of-a-data-binding

[slawomir-brzezinski-at-interxion]

@TimvdLippe Using $value can't work with <textarea> because there isn't such an attribute.

If this was static HTML, you'd pass the value <textarea>here</textarea> but this doesn't work with two-way binding.
Rather, there exists a value property and binding to it is the Polymer prescribed pattern

[TimvdLippe]

@slawomir-brzezinski-at-interxion Oh sorry I missed that. Yeah seems like a bug.

[kevinpschaaf]

Thanks for the issue. Interesting that it's the first bug report we've had of this, even though Polymer 1.0 would have suffered from the same issue.

At any rate, we avoid this for <input>.value only because there's an explicit special-case check for that exact case in the binding code: https://github.com/Polymer/polymer/blob/master/lib/mixins/property-effects.html#L601

Since we've already got precedent for special-casing input, I think we'd just add an || node.localName == textarea' to the condition and fix the bug.

[slawomir-brzezinski-at-interxion]

Thanks for fixing this guys.
@azakus does this fix 1.X at all?