Directive ngValue sometimes do not update value attribute

[dmytro-krekota]

• It is a bug.

• Current behavior: directive ngValue sometimes do not update value attribute. In my examples below, I clear $rootScope.someText value with delete operator (or set $rootScope.someText to undefined) and ngValue directive do not update view value.

• Demo:
  Example in CodePen: https://codepen.io/dmitry_krekota/pen/NdNYjr
  Screen record with bug reproduce steps (12 seconds): https://drive.google.com/file/d/0Bxtv10NlSOEbeXJWWnhZc1A0anM/view
  Also, you can download the html file with demo: https://cl.ly/1h0F3l2P032K/download/demo.html

• Expected behavior: ngValue must set attribute value to '', when when there is no value in $rootScope.someText variable.

• Environment: Windows 7, Chrome 56

• Angular version: 1.6.1

[gkalpak]

This happens because of e6afca0.

Theoretically, when the value changes to undefined (either via delete $rootScope.someText or $rootScope.someText = undefined), the value attribute should be removed and the value property should be set to undefined (which essentially sets it to '' for <input> elements.

The problem is that element.prop('value', undefined) does not work as expected, because jqLite treats it in the same way as element.prop('value') (the getter). For example, $rootScope.someText = null works as expected.

I wonder how jQuery handles that...

[gkalpak]

jQuery handles it in th same way (.prop('value', undefined) is the same as .prop('value')). It seems we need special logic inside ngValue to convert undefined values to null (or something).