Rolling forward https://codereview.chromium.org/1155683008/ which was

third_party/polymer/v0_8/components-chromium/iron-form/iron-form-extracted.js

-
-/*
-``<iron-form>` is an HTML `<form>` element that can validate and submit any custom
-elements that implement `Polymer.IronFormElementBehavior`, as well as any
-native HTML elements.
-
-It supports both `get` and `post` methods, and uses an `iron-ajax` element to
-submit the form data to the action URL.
-
-  Example:
-
-    <form is="iron-form" id="form" method="post" action="/form/handler">
-      <paper-input name="name" label="name"></paper-input>
-      <input name="address">
-      ...
-    </form>
-
-By default, a native `<button>` element will submit this form. However, if you
-want to submit it from a custom element's click handler, you need to explicitly
-call the form's `submit` method.
-
-  Example:
-
-    <paper-button raised onclick="submitForm()">Submit</paper-button>
-
-    function submitForm() {
-      document.getElementById('form').submit();
-    }
-    
-@demo demo/index.html
-*/
-
-  Polymer({
-
-    is: 'iron-form',
-
-    extends: 'form',
-
-    /**
-     * Fired after the form is submitted.
-     *
-     * @event iron-form-submit
-     */
-
-    /**
-    * Fired after the form is submitted and a response is received.
-    *
-    * @event iron-form-response
-    */
-
-    /**
-     * Fired after the form is submitted and an error is received.
-     *
-     * @event iron-form-error
-     */
-
-    listeners: {
-      'iron-form-element-register': '_registerElement',
-      'submit': 'submit'
-    },
-
-    ready: function() {
-      // Object that handles the ajax form submission request.
-      this._requestBot = document.createElement('iron-ajax');
-      this._requestBot.addEventListener('response', this._handleFormResponse.bind(this));
-      this._requestBot.addEventListener('error', this._handleFormError.bind(this));
-
-      // Holds all the custom elements registered with this form.
-      this._customElements = [];
-    },
-
-    /**
-     * Called to submit the form.
-     */
-    submit: function(event) {
-      if (!this._validate()) {
-        return false;
-      }
-
-      var json = this.serialize();
-
-      this._requestBot.url = this.action;
-      this._requestBot.method = this.method;
-      this._requestBot.params = json;
-
-      if (this.method == 'POST') {
-        this._requestBot.body = JSON.stringify(json);
-      }
-
-      this._requestBot.generateRequest();
-      this.fire('iron-form-submit', json);
-
-      // Don't perform a page refresh.
-      if (event) {
-        event.preventDefault();
-      }
-
-      return false;
-    },
-
-    /**
-     * Returns a json object containing name/value pairs for all the registered
-     * custom components and native elements of the form. If there are elements
-     * with duplicate names, then their values will get aggregated into an
-     * array of values.
-     */
-    serialize: function() {
-      var json = {};
-
-      function addSerializedElement(el) {
-        // If the name doesn't exist, add it. Otherwise, serialize it to
-        // an array,
-        if (!json[el.name]) {
-          json[el.name] = el.value;
-        } else {
-          if (!Array.isArray(json[el.name])) {
-            json[el.name] = [json[el.name]];
-          }
-          json[el.name].push(el.value);
-        }
-      }
-
-      // Go through all of the registered custom components.
-      for (var el, i = 0; el = this._customElements[i], i < this._customElements.length; i++) {
-        if (el.name) {
-          addSerializedElement(el);
-        }
-      }
-
-      // Also go through the form's native elements.
-      for (var el, i = 0; el = this.elements[i], i < this.elements.length; i++) {
-        // Checkboxes and radio buttons should only use their value if they're checked.
-        // Also, custom elements that extend native elements (like an
-        // `<input is="fancy-input">`) will appear in both lists. Since they
-        // were already added as a custom element, they don't need
-        // to be re-added.
-        if (!el.name || !this._useValue(el) ||
-            (el.hasAttribute('is') && json[el.name])) {
-          continue;
-        }
-        addSerializedElement(el);
-      }
-
-      return json;
-    },
-
-    _handleFormResponse: function (event) {
-      this.fire('iron-form-response', event.detail.response);
-    },
-
-    _handleFormError: function (event) {
-      this.fire('iron-form-error', event.detail);
-    },
-
-    _registerElement: function(e) {
-      this._customElements.push(e.target);
-    },
-
-    _validate: function() {
-      var valid = true;
-      for (var el, i = 0; el = this._customElements[i], i < this._customElements.length; i++) {
-        valid = el.validate() && valid;
-      }
-      return valid;
-    },
-
-    _useValue: function(el) {
-      // Checkboxes and radio buttons should only use their value if they're checked.
-      if (el.type !== 'checkbox' && el.type !== 'radio') {
-        return true;
-      } else {
-        return el.checked;
-      }
-    }
-
-  });
-