Polymer 1.0: How to pass an argument to a Polymer

Question

Is there a way to pass an argument to a Polymer function from an element attribute inside its <template>?

<script src="http://www.polymer-project.org/1.0/samples/components/webcomponentsjs/webcomponents-lite.js"></script>
<link rel="import" href="http://www.polymer-project.org/1.0/samples/components/polymer/polymer.html" />
<dom-module id="example-element">
  <template>
    ...
    <paper-button id="foo" on-tap="bar">Click</paper-button>
    ...
  </template>
</dom-module>
<script>
  (function() {
    Polymer({
      is: 'example-element',
      properties: {...},
      bar: function(arg){
        // Do stuff using argument arg
      }
    });
  })();
</script>

Background Research

I have combed through the documentation which appears silent on the matter. It doesn't say whether you can or can not. But when I try it, it fails. But maybe I'm not doing it correctly. So I need some assistance.

The only thing I have come across is event listeners which doesn't seem to be able to take the arguments I want to pass. Say, an id or a name.

Previous Attempts

I have tried (unsuccessfully) doing things like:

<paper-button id="foo" on-tap="bar('foo')"> Click </paper-button>

but nothing seems to work.

The event listeners idea doesn't work because they limit the arguments and I can't get the, say, id I need.

Answer 1

You could utilize HTML5 data attributes instead. Try like this:

<paper-button id="foo" on-tap="bar" data-args="foo,some other value,2">Click</paper-button>
...
<script>
(function() {
  Polymer({
    is: 'example',
    properties: {...},
    bar: function(e){
      var args = e.target.getAttribute('data-args').split(',');
      // now args = ['foo', 'some other value', '2']
    }
  });
})();
</script>

Answer 2

Shining more light on a subtle difference mentioned in the comments above.

Notice $= must be used if reading a data binding.

<paper-button on-tap="_handleTap" data-foo="foo" data-bar$="[[bar]]">Tap</paper-button>

...

_handleTap: function(e) {
  var foo = e.target.dataset.foo;
  var bar = e.target.dataset.bar;
}

Inside dom-repeat, the item (or whichever name you give it) is available at e.model.item.

<template is="dom-repeat" items="[[items]]" as="someItem">
  <paper-button on-tap="_handleTap">Tap</paper-button>
</template>

...

_handleTap: function(e) {
  var item = e.model.someItem;
}

Answer 3

Just now I got this to work:

<paper-button id="foo" on-tap="bar" data-args="baz,qux,quux">Click</paper-button>
...
<script>
(function() {
  Polymer({
    is: 'example',
    properties: {...},
    bar: function(e){
      var args = e.target.dataset.args.split(','); // ['baz', 'qux', 'quux']
    }
  });
})();
</script>

Answer 4

Depending on the situation, the clean way to do this is usually using dom-repeat. If you can format your data as an array of objects, you can just use e.model to get everything.

Answer 5

After searching a lot, I found what I think is the cleanest possible solution.

If the paper-button is inside a template, e.g.

<template is="dom-repeat" items="{{allItems}}" as="item">
 <paper-button on-tap="itemTapped">[[item.text]]</paper-button>
</template>

Then the properties can be accessed via "model" property in event object passed to function.

itemTapped: function(oEvent){
// oEvent.model.get is the getter for all properties of "item" in your bound array
console.log(oEvent.model.get('item.task'));
}

Answer 6

Is there a way to pass an argument to a Polymer function from an attribute of an element inside its <template>.

Instead of using an event use a computed binding. Computed bindings can accept literal strings.

Checkout the working example below. In this example a button can be hidden based on the parameter that is passed.

<script src="http://www.polymer-project.org/1.0/samples/components/webcomponentsjs/webcomponents-lite.js"></script>
<link rel="import" href="http://www.polymer-project.org/1.0/samples/components/polymer/polymer.html" />
<dom-module id="example-element">
	<template>
		<button id="foo-one" on-tap="barEvent">Click foo-one</button>
		<button id="foo-two" hidden="{{barTest('value-two')}}">Click foo-two</button>
		<button id="foo-three" hidden="{{barTest('value-three')}}">Click foo-three</button>
	</template>
</dom-module>
<script>
	Polymer({
		is: "example-element",
		barEvent: function (event) {
			console.log(event.target.id);
		},
		barTest: function (arg) {
			if (arg === "value-two") {
				return true;
			} else {
				return false;
			}
		}
	});
</script>

<example-element></example-element>

Note: You can get the id or other attributes of an element that an event is run on through event.target. If you are only looking for other attributes as parameters this might also be a valid solution.