Polymer Component not independent from each other? - polymer

Question

Given this simplified component:
<dom-module id="poly-component">
<template>
<paper-button raised onclick="dialog.open()">Button</paper-button>
<paper-dialog id="dialog"><h1>Paper Dialog Here!</h1></paper-dialog>
</template>
<script>
Polymer({
is: 'poly-component'
})
</script>
which does nothing more than open the dialog on clicking the button.
This module works when it used once on a page.
But when it is inserted twice
[...]
<dom-module id="polyTest-app">
<template>
<h2>Hello [[prop1]]</h2>
<poly-component></poly-component>
<poly-component></poly-component>
</template>
[...]
it doesn't work anymore.
A click on the button leads to a:
(index):1 Uncaught TypeError: dialog.open is not a function
Am I missing something?
The code for this example can be found here: Example Code on GitHub

Answer 1

Your code cannot work because you're not binding the event handler correctly.
A built-in handler like onclick tries to execute the bit of code in global scope where dialog doesn't exist. Hence the error.
Here's how you can rewrite your code
<dom-module id="poly-component">
<template>
<paper-button raised on-click="_dialogOpen">Button</paper-button>
<paper-dialog id="dialog"><h1>Paper Dialog Here!</h1></paper-dialog>
</template>
<script>
Polymer({
is: 'poly-component',
_dialogOpen: function() {
this.$.dialog.open();
}
})
</script>
</dom-module>
First, notice how onclick changes to on-click - the Polymer event handling notation. PS. tap event is advised.
Second, you can only access other elements from code. Not directly in bindings. Hence the _dialogOpen function.
UPDATE
Ok, I know what's happening. When there is only one element with a given id, the browsers let's you use it simply by that id in global scope.
When you use Shady DOM, which I assume you do, two instances of your poly-component element render two <dialog id="dialog">. At this point window.dialog is not available anymore.
Again, with Polymer it's safer to use the this.$ notation aka Automatic node finding to reference elements in local DOM.