On Tue, 26 Jul 2016 at 00:52 qiuyangs via Polymer <
[email protected]> wrote:
> Hi,
>
> I am having a question about Boolean property value. As the doc says Boolean
> properties are set based on the *presence* of the attribute: if the
> attribute exists at all, the property is set to true, regardless of the
> attribute *value*. If the attribute is absent, the property gets its
> default value.
>
> Here is my experiment. my-element want to use a collapseOpened property to
> bind to it's local DOM iron-collapse's property 'opened'.
>
> <iron-collapse opened="{{collapseOpened}}">
> some texts
> </iron-collapse>
>
> <script>
> Polymer({
> is: 'my-element',
>
> properties: {
> collapseOpened: {
> type: Boolean,
> value: false,
> }
> },
> });
> </script>
>
>
> Since in the 'opened' attribute is present in iron-collapse, should it be
> true? But in fact, the iron-collapse is not expanded, which indicates the
> value is false.
>
> Any ideas?
>
I believe there are two different things going-on here. You are correct
that HTML specifies that if an attribute is present then it is always a
truthy value when queried by javascript even if explicitly set to false in
the markup. The problem is that your attribute is assigned a value via
Polymer's data-binding. If this were a normal attribute on a regular HTML
specified tag such as <div hidden=""> then class would always be truthy.
However as this is a custom-element-specific attribute handled via
Polymer's data-binding then the rules are a bit less well-defined. Polymer
is explicitly setting the javascript property named for the attribute to
the value of "false" via data-binding even-though the attribute is present
in the markup.
HTH,
Dan.
Follow Polymer on Google+: plus.google.com/107187849809354688692
---
You received this message because you are subscribed to the Google Groups
"Polymer" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To view this discussion on the web visit
https://groups.google.com/d/msgid/polymer-dev/CABtuYwfhsyaCpLHk937Oy%3DEt2%2BD17sG7mfESJ75KynshukEg8Q%40mail.gmail.com.
For more options, visit https://groups.google.com/d/optout.
