refactor: remove XDomainRequest support

This was used in IE8 (but behind a flag).

BREAKING CHANGE: the enableXDR option is removed

Related: #674

Author: darrachequesne

README.md

@@ -227,7 +227,6 @@ Exposed as `eio` in the browser standalone build.
       - `upgrade` (`Boolean`): defaults to true, whether the client should try
       to upgrade the transport from long-polling to something better.
       - `forceBase64` (`Boolean`): forces base 64 encoding for polling transport even when XHR2 responseType is available and WebSocket even if the used standard supports binary.
-      - `enablesXDR` (`Boolean`): enables XDomainRequest for IE8 to avoid loading bar flashing with click sound. default to `false` because XDomainRequest has a flaw of not sending cookie.
       - `withCredentials` (`Boolean`): defaults to `false`, whether to include credentials (cookies, authorization headers, TLS client certificates, etc.) with cross-origin XHR polling requests.
       - `timestampRequests` (`Boolean`): whether to add the timestamp with each
         transport request. Note: polling requests are always stamped unless this

lib/socket.ts

@@ -53,14 +53,6 @@ export interface SocketOptions {
    */
   forceBase64: boolean;
 
-  /**
-   * Enables XDomainRequest for IE8 to avoid loading bar flashing with
-   * click sound. default to `false` because XDomainRequest has a flaw
-   * of not sending cookie.
-   * @default false
-   */
-  enablesXDR: boolean;
-
   /**
    * The param name to use as our timestamp key
    * @default 't'

lib/transports/polling-xhr.ts

@@ -148,7 +148,6 @@ export class Request extends Emitter {
     const opts = pick(
       this.opts,
       "agent",
-      "enablesXDR",
       "pfx",
       "key",
       "passphrase",
@@ -196,27 +195,18 @@ export class Request extends Emitter {
         xhr.timeout = this.opts.requestTimeout;
       }
 
-      if (this.hasXDR()) {
-        xhr.onload = () => {
+      xhr.onreadystatechange = () => {
+        if (4 !== xhr.readyState) return;
+        if (200 === xhr.status || 1223 === xhr.status) {
           this.onLoad();
-        };
-        xhr.onerror = () => {
-          this.onError(xhr.responseText);
-        };
-      } else {
-        xhr.onreadystatechange = () => {
-          if (4 !== xhr.readyState) return;
-          if (200 === xhr.status || 1223 === xhr.status) {
-            this.onLoad();
-          } else {
-            // make sure the `error` event handler that's user-set
-            // does not throw in the same tick and gets caught here
-            this.setTimeoutFn(() => {
-              this.onError(typeof xhr.status === "number" ? xhr.status : 0);
-            }, 0);
-          }
-        };
-      }
+        } else {
+          // make sure the `error` event handler that's user-set
+          // does not throw in the same tick and gets caught here
+          this.setTimeoutFn(() => {
+            this.onError(typeof xhr.status === "number" ? xhr.status : 0);
+          }, 0);
+        }
+      };
 
       debug("xhr data %s", this.data);
       xhr.send(this.data);
@@ -275,12 +265,7 @@ export class Request extends Emitter {
     if ("undefined" === typeof this.xhr || null === this.xhr) {
       return;
     }
-    // xmlhttprequest
-    if (this.hasXDR()) {
-      this.xhr.onload = this.xhr.onerror = empty;
-    } else {
-      this.xhr.onreadystatechange = empty;
-    }
+    this.xhr.onreadystatechange = empty;
 
     if (fromError) {
       try {
@@ -307,16 +292,6 @@ export class Request extends Emitter {
     }
   }
 
-  /**
-   * Check if it has XDomainRequest.
-   *
-   * @api private
-   */
-  hasXDR() {
-    // @ts-ignore
-    return typeof XDomainRequest !== "undefined" && !this.xs && this.enablesXDR;
-  }
-
   /**
    * Aborts the request.
    *

lib/xmlhttprequest.ts

@@ -6,32 +6,13 @@ import globalThis from "./globalThis.js";
 export default function(opts) {
   const xdomain = opts.xdomain;
 
-  // scheme must be same when usign XDomainRequest
-  // http://blogs.msdn.com/b/ieinternals/archive/2010/05/13/xdomainrequest-restrictions-limitations-and-workarounds.aspx
-  const xscheme = opts.xscheme;
-
-  // XDomainRequest has a flow of not sending cookie, therefore it should be disabled as a default.
-  // https://github.com/Automattic/engine.io-client/pull/217
-  const enablesXDR = opts.enablesXDR;
-
   // XMLHttpRequest can be disabled on IE
   try {
     if ("undefined" !== typeof XMLHttpRequest && (!xdomain || hasCORS)) {
       return new XMLHttpRequest();
     }
   } catch (e) {}
 
-  // Use XDomainRequest for IE8 if enablesXDR is true
-  // because loading bar keeps flashing when using jsonp-polling
-  // https://github.com/yujiosaka/socke.io-ie8-loading-example
-  try {
-    // @ts-ignore
-    if ("undefined" !== typeof XDomainRequest && !xscheme && enablesXDR) {
-      // @ts-ignore
-      return new XDomainRequest();
-    }
-  } catch (e) {}
-
   if (!xdomain) {
     try {
       return new globalThis[["Active"].concat("Object").join("X")](

test/index.js

@@ -13,7 +13,6 @@ require("./engine.io-client");
 require("./socket");
 require("./transport");
 require("./connection");
-require("./transports");
 require("./xmlhttprequest");
 
 if (typeof ArrayBuffer !== "undefined") {

test/support/env.js

@@ -14,7 +14,6 @@ exports.wsSupport = !!(
 const userAgent = typeof navigator !== "undefined" ? navigator.userAgent : "";
 exports.isOldSimulator =
   ~userAgent.indexOf("iPhone OS 4") || ~userAgent.indexOf("iPhone OS 5");
-exports.isIE8 = /MSIE 8/.test(userAgent);
 exports.isIE9 = /MSIE 9/.test(userAgent);
 exports.isIE10 = /MSIE 10/.test(userAgent);
 exports.isIE11 = !!userAgent.match(/Trident.*rv[ :]*11\./); // ws doesn't work at all in sauce labs

test/transports/index.js

@@ -3,7 +3,7 @@ const XMLHttpRequest = require("../build/cjs/xmlhttprequest").default;
 const env = require("./support/env");
 
 describe("XMLHttpRequest", () => {
-  if (env.isIE8 || env.isIE9) {
+  if (env.isIE9) {
     describe("IE8_9", () => {
       context("when xdomain is false", () => {
         it("should have same properties as XMLHttpRequest does", () => {