Shared behavior state across custom elements

Question

Shared behavior state across custom elements

1.1k views Asked by losttime At 10 June 2015 at 04:04

I have these two custom Polymer Elements (Polymer 1.0.3):

Displays text to be translated.
Displays button to trigger loading of translation.

I also have a Behavior that holds the translations (json object) and contains all the functions that make translation possible.

This is what I expect to happen:

Click the button in Element 2
Translations load into the Behavior
Language selection is set in the Behavior
Text in Element 1 is updated with the translated equivalent

Steps 1 - 3 happen, but 4 doesn't. The text is never updated. I can get it to work if Elements 1 & 2 are combined as the same element, but not if they're separate (any they need to be separate).

If you're wondering about the "kick" property, it's something I learned from Polymer 0.5. It got things working when the two elements were combined, so I'm thinking it'll be be necessary when the elements are separate.

Any idea how I can make this happen? I'm open to alternative paradigms.

Code

This is roughly how my code is laid out. I also made a plunker with a single-page test case.

index.html

<!doctype html>
<html>

<head>
  <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">
  <link rel="import" href="behavior.html">
  <link rel="import" href="element1.html">
  <link rel="import" href="element2.html">
</head>

<body>
  <my-element></my-element>
  <another-element></another-element>
</body>

</html>

Element 1

<dom-module id="my-element">
  <template>
    <p>{{localize(label, kick)}}</p>
  </template>
</dom-module>

<script>
  Polymer({
    is: 'my-element',
    behaviors: [
      behavior
    ],
    properties: {
      label: {
        type: String,
        value: 'original'
      }
    }
  });
</script>

Element 2

<dom-module id="another-element">
  <template>
    <button on-click="buttonClicked">load</button>
  </template>
</dom-module>
<script>
  Polymer({
    is: 'another-element',
    behaviors: [
      behavior
    ],
    buttonClicked: function() {
      this.registerTranslation('en', {
        original: 'changed'
      })
      this.selectLanguage('en');
    }
  });
</script>

Behavior

<script>
  var behavior = {
    properties: {
      kick: {
        type: Number,
        value: 0
      },
      language: {
        type: String,
        value: 'fun'
      },
      translations: {
        type: Object,
        value: function() {
          return {};
        }
      }
    },
    localize: function(key, i) {
      if (this.translations[this.language] && this.translations[this.language][key]) {
        return this.translations[this.language][key];
      }
      return key;
    },
    registerTranslation: function(translationKey, translationSet) {
      this.translations[translationKey] = translationSet;
    },
    selectLanguage: function(newLanguage) {
      this.language = newLanguage;
      this.set('kick', this.kick + 1);
    }
  };
</script>

Original Q&A

There are 1 answers

**Scott Miles** · Accepted Answer · 2015-06-10 12:45:50

First, although the notion is to have behavior be a conduit for shared data between instances, as written, each instance will have it's own copy of the translations object and the kick property.

Second, even if that data was privatized so it could be shared, the kick binding made via localize(label, kick) is in a different scope from the expression that modifies kick (i.e. this.set('kick', this.kick + 1); [{sic} this could simply be this.kick++;]).

To notify N instances of a change in shared data, one must keep track of those instances. A good way to do this is by attaching event listeners. Another way is simply keeping a list.

Here is an example implementation of your design:

    <script>
      (function() {
        var instances = [];
        var translationDb = {};
        var language = '';

        window.behavior = {
          properties: {
            l10n: {
              value: 0
            }  
          },
          attached: function() {
            instances.push(this);
          },
          detached: function() {
            this.arrayDelete(instances, this);
          },
          _broadcast: function() {
            instances.forEach(function(i) {
              i.l10n++;
            });
          },
          localize: function(key, i) {
            if (translationDb[language] && translationDb[language][key]) {
              return translationDb[language][key];
            }
            return key;
          },
          registerTranslation: function(translationKey, translationSet) {
            translationDb[translationKey] = translationSet;
          },
          selectLanguage: function(newLanguage) {
            language = newLanguage;
            this._broadcast();
          }
        };
      })();
  </script>

  <dom-module id="my-element">
    <template>
      <p>{{localize(label, l10n)}}</p>
    </template>
    <script>
      Polymer({
        behaviors: [
          behavior
        ],
        properties: {
          label: {
            type: String,
            value: 'original'
          }
        }
      });
    </script>
  </dom-module>

  <dom-module id="another-element">
    <template>
      <button on-tap="buttonClicked">load</button>
    </template>
    <script>
      Polymer({
        behaviors: [
          behavior
        ],
        buttonClicked: function() {
          this.registerTranslation('en', {
            original: 'changed'
          });
          this.selectLanguage('en');
        }
      });
    </script>
  </dom-module>

TechQA.

Shared behavior state across custom elements

Code

index.html

Element 1

Element 2

Behavior

There are 1 answers

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