readmongo/node_modules/engine.io-client/lib/transports/polling-jsonp.js

const Polling = require("./polling");
const globalThis = require("../globalThis");

const rNewline = /\n/g;
const rEscapedNewline = /\\n/g;

/**
 * Global JSONP callbacks.
 */

let callbacks;

/**
 * Noop.
 */

function empty() {}

class JSONPPolling extends Polling {
  /**
   * JSONP Polling constructor.
   *
   * @param {Object} opts.
   * @api public
   */
  constructor(opts) {
    super(opts);

    this.query = this.query || {};

    // define global callbacks array if not present
    // we do this here (lazily) to avoid unneeded global pollution
    if (!callbacks) {
      // we need to consider multiple engines in the same page
      callbacks = globalThis.___eio = globalThis.___eio || [];
    }

    // callback identifier
    this.index = callbacks.length;

    // add callback to jsonp global
    const self = this;
    callbacks.push(function(msg) {
      self.onData(msg);
    });

    // append to query string
    this.query.j = this.index;

    // prevent spurious errors from being emitted when the window is unloaded
    if (typeof addEventListener === "function") {
      addEventListener(
        "beforeunload",
        function() {
          if (self.script) self.script.onerror = empty;
        },
        false
      );
    }
  }

  /**
   * JSONP only supports binary as base64 encoded strings
   */
  get supportsBinary() {
    return false;
  }

  /**
   * Closes the socket.
   *
   * @api private
   */
  doClose() {
    if (this.script) {
      this.script.parentNode.removeChild(this.script);
      this.script = null;
    }

    if (this.form) {
      this.form.parentNode.removeChild(this.form);
      this.form = null;
      this.iframe = null;
    }

    super.doClose();
  }

  /**
   * Starts a poll cycle.
   *
   * @api private
   */
  doPoll() {
    const self = this;
    const script = document.createElement("script");

    if (this.script) {
      this.script.parentNode.removeChild(this.script);
      this.script = null;
    }

    script.async = true;
    script.src = this.uri();
    script.onerror = function(e) {
      self.onError("jsonp poll error", e);
    };

    const insertAt = document.getElementsByTagName("script")[0];
    if (insertAt) {
      insertAt.parentNode.insertBefore(script, insertAt);
    } else {
      (document.head || document.body).appendChild(script);
    }
    this.script = script;

    const isUAgecko =
      "undefined" !== typeof navigator && /gecko/i.test(navigator.userAgent);

    if (isUAgecko) {
      setTimeout(function() {
        const iframe = document.createElement("iframe");
        document.body.appendChild(iframe);
        document.body.removeChild(iframe);
      }, 100);
    }
  }

  /**
   * Writes with a hidden iframe.
   *
   * @param {String} data to send
   * @param {Function} called upon flush.
   * @api private
   */
  doWrite(data, fn) {
    const self = this;
    let iframe;

    if (!this.form) {
      const form = document.createElement("form");
      const area = document.createElement("textarea");
      const id = (this.iframeId = "eio_iframe_" + this.index);

      form.className = "socketio";
      form.style.position = "absolute";
      form.style.top = "-1000px";
      form.style.left = "-1000px";
      form.target = id;
      form.method = "POST";
      form.setAttribute("accept-charset", "utf-8");
      area.name = "d";
      form.appendChild(area);
      document.body.appendChild(form);

      this.form = form;
      this.area = area;
    }

    this.form.action = this.uri();

    function complete() {
      initIframe();
      fn();
    }

    function initIframe() {
      if (self.iframe) {
        try {
          self.form.removeChild(self.iframe);
        } catch (e) {
          self.onError("jsonp polling iframe removal error", e);
        }
      }

      try {
        // ie6 dynamic iframes with target="" support (thanks Chris Lambacher)
        const html = '<iframe src="javascript:0" name="' + self.iframeId + '">';
        iframe = document.createElement(html);
      } catch (e) {
        iframe = document.createElement("iframe");
        iframe.name = self.iframeId;
        iframe.src = "javascript:0";
      }

      iframe.id = self.iframeId;

      self.form.appendChild(iframe);
      self.iframe = iframe;
    }

    initIframe();

    // escape \n to prevent it from being converted into \r\n by some UAs
    // double escaping is required for escaped new lines because unescaping of new lines can be done safely on server-side
    data = data.replace(rEscapedNewline, "\\\n");
    this.area.value = data.replace(rNewline, "\\n");

    try {
      this.form.submit();
    } catch (e) {}

    if (this.iframe.attachEvent) {
      this.iframe.onreadystatechange = function() {
        if (self.iframe.readyState === "complete") {
          complete();
        }
      };
    } else {
      this.iframe.onload = complete;
    }
  }
}

module.exports = JSONPPolling;