test-fixture.html

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<script>
(function () {
  var TestFixturePrototype = Object.create(HTMLElement.prototype);
  var TestFixtureExtension = {
    _fixtureTemplates: null,

    _elementsFixtured: false,

    get elementsFixtured () {
      return this._elementsFixtured;
    },

    get fixtureTemplates () {
      if (!this._fixtureTemplates) {
        this._fixtureTemplates = this.querySelectorAll('template');
      }

      return this._fixtureTemplates;
    },

    create: function (model) {
      var generatedDoms = [];

      this.restore();

      this.removeElements(this.fixtureTemplates);

      this.forElements(this.fixtureTemplates, function (fixtureTemplate) {
        generatedDoms.push(
          this.createFrom(fixtureTemplate, model)
        );
      }, this);

      if (generatedDoms.length < 2) {
        return generatedDoms[0];
      }

      return generatedDoms;
    },

    createFrom: function (fixtureTemplate, model) {
      var fixturedFragment;
      var fixturedElements;
      var fixturedElement;

      if (!(fixtureTemplate &&
            fixtureTemplate.tagName === 'TEMPLATE')) {
        return;
      }

      try {
        fixturedFragment = this.stamp(fixtureTemplate, model);
      } catch (error) {
        console.error('Error stamping', fixtureTemplate, error);
        throw error;
      }

      fixturedElements = this.collectElementChildren(fixturedFragment);

      this.appendChild(fixturedFragment);
      this._elementsFixtured = true;

      if (fixturedElements.length < 2) {
        return fixturedElements[0];
      }

      return fixturedElements;
    },

    restore: function () {
      if (!this._elementsFixtured) {
        return;
      }

      this.removeElements(this.children);

      this.forElements(this.fixtureTemplates, function (fixtureTemplate) {
        this.appendChild(fixtureTemplate);
      }, this);

      this.generatedDomStack = [];

      this._elementsFixtured = false;
    },

    collectElementChildren: function (parent) {
      // Note: Safari 7.1 does not support `firstElementChild` or
      // `nextElementSibling`, so we do things the old-fashioned way:
      var elements = [];
      var child = parent.firstChild;

      while (child) {
        if (child.nodeType !== Node.TEXT_NODE) {
          elements.push(child);
        }

        child = child.nextSibling;
      }

      return elements;
    },

    removeElements: function (elements) {
      this.forElements(elements, function (element) {
        this.removeChild(element);
      }, this);
    },

    forElements: function (elements, iterator, context) {
      Array.prototype.slice.call(elements)
        .forEach(iterator, context);
    },

    stamp: function (fixtureTemplate, model) {
      var stamped;
      // Check if we are dealing with a "stampable" `<template>`. This is a
      // vaguely defined special case of a `<template>` that is a custom
      // element with a public `stamp` method that implements some manner of
      // data binding.
      if (fixtureTemplate.stamp) {
        stamped = fixtureTemplate.stamp(model);
        // We leak Polymer specifics a little; if there is an element `root`, we
        // want that to be returned.
        stamped = stamped.root || stamped;

      // Otherwise, we fall back to standard HTML templates, which do not have
      // any sort of binding support.
      } else {
        if (model) {
          console.warn(this, 'was given a model to stamp, but the template is not of a bindable type');
        }

        stamped = document.importNode(fixtureTemplate.content, true);

        // Immediately upgrade the subtree if we are dealing with async
        // Web Components polyfill.
        // https://github.com/Polymer/polymer/blob/0.8-preview/src/features/mini/template.html#L52
        if (window.CustomElements && CustomElements.upgradeSubtree) {
          CustomElements.upgradeSubtree(stamped);
        }
      }

      return stamped;
    }
  };

  Object.getOwnPropertyNames(TestFixtureExtension)
    .forEach(function (property) {
      Object.defineProperty(
        TestFixturePrototype,
        property,
        Object.getOwnPropertyDescriptor(TestFixtureExtension, property)
      );
    });

  document.registerElement('test-fixture', {
    prototype: TestFixturePrototype
  });
})();
</script>