Allow cross origin - iron-ajax - Polymer
<pre><code>XMLHttpRequest cannot load http://abcd.com/xyz?id=1. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:8080' is therefore not allowed access.
</code></pre>

<p>I'm setting  </p>

<pre><code>&lt;iron-ajax
                id="requestRepos"
                headers='{"Accept": "*/*"}'
                url="http://abcd.com/xyz"
                params="{{requestParams}}"
                handle-as="json"
                on-response="handleResponse"&gt;&lt;/iron-ajax&gt;
</code></pre>

<p>I tried the above using <code>CORS</code> extension in chrome, and it worked. But without it, it doesn't work.</p>

<p>Below is the start_server.js file</p>

<pre><code>/**
 * @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
 * subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
 */
"use strict";
const express = require('express');
const http = require('http');
const path = require('path');
const send = require('send');
const url = require('url');
const make_app_1 = require('./make_app');
const findPort = require('find-port');
const opn = require('opn');
function applyDefaultOptions(options) {
    const withDefaults = Object.assign({}, options);
    Object.assign(withDefaults, {
        port: options.port || 8080,
        hostname: options.hostname || "localhost",
        root: path.resolve(options.root || '.'),
    });
    return withDefaults;
}
/**
 * @return {Promise} A Promise that completes when the server has started.
 */
function startServer(options) {
    return new Promise((resolve, reject) =&gt; {
        options = options || {};
        if (options.port) {
            resolve(options);
        }
        else {
            findPort(8080, 8180, (ports) =&gt; {
                options.port = ports[0];
                resolve(options);
            });
        }
    }).then((opts) =&gt; startWithPort(opts));
}
exports.startServer = startServer;
const portInUseMessage = (port) =&gt; `
ERROR: Port in use: ${port}
Please choose another port, or let an unused port be chosen automatically.
`;
function getApp(options) {
    const port = options.port;
    const hostname = options.hostname;
    const root = options.root;
    const app = express();
    console.log(`Starting Polyserve...
    serving on port: ${port}
    from root: ${root}
  `);
    const polyserve = make_app_1.makeApp({
        componentDir: options.componentDir,
        packageName: options.packageName,
        root,
    });
    options.packageName = polyserve.packageName;
    const filePathRegex = /.*\/.+\..{1,}$/;
    app.use('/components/', polyserve);
    app.use(function(req, res, next) {
  res.header("Access-Control-Allow-Origin", "*");
  res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
  next();
});
    app.get('/*', (req, res) =&gt; {
        const filePath = req.path;
        send(req, filePath, { root: root, })
            .on('error', (error) =&gt; {
            if ((error).status == 404 &amp;&amp; !filePathRegex.test(filePath)) {
                send(req, '/', { root: root }).pipe(res);
            }
            else {
                res.statusCode = error.status || 500;
                res.end(error.message);
            }
        })
            .pipe(res);
    });
    return app;
}
exports.getApp = getApp;
/**
 * Open the given web page URL. If no browser keyword is provided, `opn` will use
 * the user's default browser.
 */
function openWebPage(url, withBrowser) {
    const openOptions = {
        app: withBrowser
    };
    opn(url, openOptions, (err) =&gt; {
        if (err) {
            // log error and continue
            console.error(`ERROR: Problem launching "${openOptions.app || 'default web browser'}".`);
        }
    });
}
function startWithPort(userOptions) {
    const options = applyDefaultOptions(userOptions);
    const app = getApp(options);
    let server = http.createServer(app);
    let serverStartedResolve;
    let serverStartedReject;
    const serverStartedPromise = new Promise((resolve, reject) =&gt; {
        serverStartedResolve = resolve;
        serverStartedReject = reject;
    });
    server = app.listen(options.port, options.hostname, () =&gt; serverStartedResolve(server));
    server.on('error', function (err) {
        if (err.code === 'EADDRINUSE') {
            console.error(portInUseMessage(options.port));
        }
        serverStartedReject(err);
    });
    const serverUrl = {
        protocol: 'http',
        hostname: options.hostname,
        port: `${options.port}`,
    };
    const componentUrl = Object.assign({}, serverUrl);
    componentUrl.pathname = `components/${options.packageName}/`;
    console.log(`Files in this directory are available under the following URLs
    applications: ${url.format(serverUrl)}
    reusable components: ${url.format(componentUrl)}`);
    if (options.open) {
        let openUrl;
        if (options.openPath) {
            openUrl = Object.assign({}, serverUrl);
            openUrl.pathname = options.openPath;
        }
        else {
            openUrl = Object.assign({}, componentUrl);
        }
        if (!Array.isArray(options.browser)) {
            openWebPage(url.format(openUrl));
        }
        else {
            options.browser.forEach((browser) =&gt; {
                openWebPage(url.format(openUrl), browser);
            });
        }
    }
    return serverStartedPromise;
}
</code></pre>