iron-ajax.html

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@license
Copyright (c) 2015 The Polymer Project Authors. All rights reserved.
This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
Code distributed by Google as part of the polymer project is also
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-->

<link rel="import" href="../polymer/polymer.html">
<link rel="import" href="iron-request.html">

<!--
The `iron-ajax` element exposes network request functionality.

    <iron-ajax
        auto
        url="https://www.googleapis.com/youtube/v3/search"
        params='{"part":"snippet", "q":"polymer", "key": "YOUTUBE_API_KEY", "type": "video"}'
        handle-as="json"
        on-response="handleResponse"
        debounce-duration="300"></iron-ajax>

With `auto` set to `true`, the element performs a request whenever
its `url`, `params` or `body` properties are changed. Automatically generated
requests will be debounced in the case that multiple attributes are changed
sequentially.

Note: The `params` attribute must be double quoted JSON.

You can trigger a request explicitly by calling `generateRequest` on the
element.

@demo demo/index.html
@hero hero.svg
-->

<script>
  'use strict';

  Polymer({

    is: 'iron-ajax',

    /**
     * Fired before a request is sent.
     *
     * @event iron-ajax-presend
     */

    /**
     * Fired when a request is sent.
     *
     * @event request
     * @event iron-ajax-request
     */

    /**
     * Fired when a response is received.
     *
     * @event response
     * @event iron-ajax-response
     */

    /**
     * Fired when an error is received.
     *
     * @event error
     * @event iron-ajax-error
     */

    hostAttributes: {
      hidden: true
    },

    properties: {
      /**
       * The URL target of the request.
       */
      url: {
        type: String
      },

      /**
       * An object that contains query parameters to be appended to the
       * specified `url` when generating a request. If you wish to set the body
       * content when making a POST request, you should use the `body` property
       * instead.
       */
      params: {
        type: Object,
        value: function() {
          return {};
        }
      },

      /**
       * The HTTP method to use such as 'GET', 'POST', 'PUT', or 'DELETE'.
       * Default is 'GET'.
       */
      method: {
        type: String,
        value: 'GET'
      },

      /**
       * HTTP request headers to send.
       *
       * Example:
       *
       *     <iron-ajax
       *         auto
       *         url="http://somesite.com"
       *         headers='{"X-Requested-With": "XMLHttpRequest"}'
       *         handle-as="json"></iron-ajax>
       *
       * Note: setting a `Content-Type` header here will override the value
       * specified by the `contentType` property of this element.
       */
      headers: {
        type: Object,
        value: function() {
          return {};
        }
      },

      /**
       * Content type to use when sending data. If the `contentType` property
       * is set and a `Content-Type` header is specified in the `headers`
       * property, the `headers` property value will take precedence.
       *
       * Varies the handling of the `body` param.
       */
      contentType: {
        type: String,
        value: null
      },

      /**
       * Body content to send with the request, typically used with "POST"
       * requests.
       *
       * If body is a string it will be sent unmodified.
       *
       * If Content-Type is set to a value listed below, then
       * the body will be encoded accordingly.
       *
       *    * `content-type="application/json"`
       *      * body is encoded like `{"foo":"bar baz","x":1}`
       *    * `content-type="application/x-www-form-urlencoded"`
       *      * body is encoded like `foo=bar+baz&x=1`
       *
       * Otherwise the body will be passed to the browser unmodified, and it
       * will handle any encoding (e.g. for FormData, Blob, ArrayBuffer).
       *
       * @type (ArrayBuffer|ArrayBufferView|Blob|Document|FormData|null|string|undefined|Object)
       */
      body: {
        type: Object,
        value: null
      },

      /**
       * Toggle whether XHR is synchronous or asynchronous. Don't change this
       * to true unless You Know What You Are Doing™.
       */
      sync: {
        type: Boolean,
        value: false
      },

      /**
       * Specifies what data to store in the `response` property, and
       * to deliver as `event.detail.response` in `response` events.
       *
       * One of:
       *
       *    `text`: uses `XHR.responseText`.
       *
       *    `xml`: uses `XHR.responseXML`.
       *
       *    `json`: uses `XHR.responseText` parsed as JSON.
       *
       *    `arraybuffer`: uses `XHR.response`.
       *
       *    `blob`: uses `XHR.response`.
       *
       *    `document`: uses `XHR.response`.
       */
      handleAs: {
        type: String,
        value: 'json'
      },

      /**
       * Set the withCredentials flag on the request.
       */
      withCredentials: {
        type: Boolean,
        value: false
      },

      /**
       * Set the timeout flag on the request.
       */
      timeout: {
        type: Number,
        value: 0
      },

      /**
       * If true, automatically performs an Ajax request when either `url` or
       * `params` changes.
       */
      auto: {
        type: Boolean,
        value: false
      },

      /**
       * If true, error messages will automatically be logged to the console.
       */
      verbose: {
        type: Boolean,
        value: false
      },

      /**
       * The most recent request made by this iron-ajax element.
       */
      lastRequest: {
        type: Object,
        notify: true,
        readOnly: true
      },

      /**
       * True while lastRequest is in flight.
       */
      loading: {
        type: Boolean,
        notify: true,
        readOnly: true
      },

      /**
       * lastRequest's response.
       *
       * Note that lastResponse and lastError are set when lastRequest finishes,
       * so if loading is true, then lastResponse and lastError will correspond
       * to the result of the previous request.
       *
       * The type of the response is determined by the value of `handleAs` at
       * the time that the request was generated.
       *
       * @type {Object}
       */
      lastResponse: {
        type: Object,
        notify: true,
        readOnly: true
      },

      /**
       * lastRequest's error, if any.
       *
       * @type {Object}
       */
      lastError: {
        type: Object,
        notify: true,
        readOnly: true
      },

      /**
       * An Array of all in-flight requests originating from this iron-ajax
       * element.
       */
      activeRequests: {
        type: Array,
        notify: true,
        readOnly: true,
        value: function() {
          return [];
        }
      },

      /**
       * Length of time in milliseconds to debounce multiple automatically generated requests.
       */
      debounceDuration: {
        type: Number,
        value: 0,
        notify: true
      },

      /**
       * Prefix to be stripped from a JSON response before parsing it.
       *
       * In order to prevent an attack using CSRF with Array responses
       * (http://haacked.com/archive/2008/11/20/anatomy-of-a-subtle-json-vulnerability.aspx/)
       * many backends will mitigate this by prefixing all JSON response bodies
       * with a string that would be nonsensical to a JavaScript parser.
       *
       */
      jsonPrefix: {
        type: String,
        value: ''
      },

      /**
       * By default, iron-ajax's events do not bubble. Setting this attribute will cause its
       * request and response events as well as its iron-ajax-request, -response,  and -error
       * events to bubble to the window object. The vanilla error event never bubbles when
       * using shadow dom even if this.bubbles is true because a scoped flag is not passed with
       * it (first link) and because the shadow dom spec did not used to allow certain events,
       * including events named error, to leak outside of shadow trees (second link).
       * https://www.w3.org/TR/shadow-dom/#scoped-flag
       * https://www.w3.org/TR/2015/WD-shadow-dom-20151215/#events-that-are-not-leaked-into-ancestor-trees
       */
      bubbles: {
        type: Boolean,
        value: false
      },

      /**
       * Changes the [`completes`](iron-request#property-completes) promise chain 
       * from `generateRequest` to reject with an object
       * containing the original request, as well an error message.
       * If false (default), the promise rejects with an error message only.
       */
      rejectWithRequest: {
        type: Boolean,
        value: false
      },

      _boundHandleResponse: {
        type: Function,
        value: function() {
          return this._handleResponse.bind(this);
        }
      }
    },

    observers: [
      '_requestOptionsChanged(url, method, params.*, headers, contentType, ' +
          'body, sync, handleAs, jsonPrefix, withCredentials, timeout, auto)'
    ],

    /**
     * The query string that should be appended to the `url`, serialized from
     * the current value of `params`.
     *
     * @return {string}
     */
    get queryString () {
      var queryParts = [];
      var param;
      var value;

      for (param in this.params) {
        value = this.params[param];
        param = window.encodeURIComponent(param);

        if (Array.isArray(value)) {
          for (var i = 0; i < value.length; i++) {
            queryParts.push(param + '=' + window.encodeURIComponent(value[i]));
          }
        } else if (value !== null) {
          queryParts.push(param + '=' + window.encodeURIComponent(value));
        } else {
          queryParts.push(param);
        }
      }

      return queryParts.join('&');
    },

    /**
     * The `url` with query string (if `params` are specified), suitable for
     * providing to an `iron-request` instance.
     *
     * @return {string}
     */
    get requestUrl() {
      var queryString = this.queryString;
      var url = this.url || '';

      if (queryString) {
        var bindingChar = url.indexOf('?') >= 0 ? '&' : '?';
        return url + bindingChar + queryString;
      }

      return url;
    },

    /**
     * An object that maps header names to header values, first applying the
     * the value of `Content-Type` and then overlaying the headers specified
     * in the `headers` property.
     *
     * @return {Object}
     */
    get requestHeaders() {
      var headers = {};
      var contentType = this.contentType;
      if (contentType == null && (typeof this.body === 'string')) {
        contentType = 'application/x-www-form-urlencoded';
      }
      if (contentType) {
        headers['content-type'] = contentType;
      }
      var header;

      if (typeof this.headers === 'object') {
        for (header in this.headers) {
          headers[header] = this.headers[header].toString();
        }
      }

      return headers;
    },

    /**
     * Request options suitable for generating an `iron-request` instance based
     * on the current state of the `iron-ajax` instance's properties.
     *
     * @return {{
     *   url: string,
     *   method: (string|undefined),
     *   async: (boolean|undefined),
     *   body: (ArrayBuffer|ArrayBufferView|Blob|Document|FormData|null|string|undefined|Object),
     *   headers: (Object|undefined),
     *   handleAs: (string|undefined),
     *   jsonPrefix: (string|undefined),
     *   withCredentials: (boolean|undefined)}}
     */
    toRequestOptions: function() {
      return {
        url: this.requestUrl || '',
        method: this.method,
        headers: this.requestHeaders,
        body: this.body,
        async: !this.sync,
        handleAs: this.handleAs,
        jsonPrefix: this.jsonPrefix,
        withCredentials: this.withCredentials,
        timeout: this.timeout,
        rejectWithRequest: this.rejectWithRequest,
      };
    },

    /**
     * Performs an AJAX request to the specified URL.
     *
     * @return {!IronRequestElement}
     */
    generateRequest: function() {
      var request = /** @type {!IronRequestElement} */ (document.createElement('iron-request'));
      var requestOptions = this.toRequestOptions();

      this.push('activeRequests', request);

      request.completes.then(
        this._boundHandleResponse
      ).catch(
        this._handleError.bind(this, request)
      ).then(
        this._discardRequest.bind(this, request)
      );

      var evt = this.fire('iron-ajax-presend', {
        request: request,
        options: requestOptions
      }, {bubbles: this.bubbles, cancelable: true});

      if (evt.defaultPrevented) {
        request.abort();
        request.rejectCompletes(request);
        return request;
      }

      request.send(requestOptions);

      this._setLastRequest(request);
      this._setLoading(true);

      this.fire('request', {
        request: request,
        options: requestOptions
      }, {
        bubbles: this.bubbles,
        composed: true
      });

      this.fire('iron-ajax-request', {
        request: request,
        options: requestOptions
      }, {
        bubbles: this.bubbles,
        composed: true
      });

      return request;
    },

    _handleResponse: function(request) {
      if (request === this.lastRequest) {
        this._setLastResponse(request.response);
        this._setLastError(null);
        this._setLoading(false);
      }
      this.fire('response', request, {
        bubbles: this.bubbles,
        composed: true
      });
      this.fire('iron-ajax-response', request, {
        bubbles: this.bubbles,
        composed: true
      });
    },

    _handleError: function(request, error) {
      if (this.verbose) {
        Polymer.Base._error(error);
      }

      if (request === this.lastRequest) {
        this._setLastError({
          request: request,
          error: error,
          status: request.xhr.status,
          statusText: request.xhr.statusText,
          response: request.xhr.response
        });
        this._setLastResponse(null);
        this._setLoading(false);
      }

      // Tests fail if this goes after the normal this.fire('error', ...)
      this.fire('iron-ajax-error', {
        request: request,
        error: error
      }, {
        bubbles: this.bubbles,
        composed: true
      });

      this.fire('error', {
        request: request,
        error: error
      }, {
        bubbles: this.bubbles,
        composed: true
      });
    },

    _discardRequest: function(request) {
      var requestIndex = this.activeRequests.indexOf(request);

      if (requestIndex > -1) {
        this.splice('activeRequests', requestIndex, 1);
      }
    },

    _requestOptionsChanged: function() {
      this.debounce('generate-request', function() {
        if (this.url == null) {
          return;
        }

        if (this.auto) {
          this.generateRequest();
        }
      }, this.debounceDuration);
    },

  });
</script>