Correct bug in isStaging method. (#1125)

This PR corrects a bug in the `isStaging` method. If you were referred to a Production
site from a Staging link, `isStaging` would incorrectly report `true`. This is because
the `includes` check on the `href` would catch the Staging `referrerPageUrl`. Simply
comparring `window.location.hostname` instead of `window.location.href` fixes this.
I also did some code cleanup in this method and its test suite.

J=SLAP-2546
TEST=auto

package.json

@@ -82,6 +82,9 @@
     "modulePathIgnorePatterns": [
       "/test-site/"
     ],
+    "transformIgnorePatterns": [
+      "!node_modules/escape-string-regexp"
+    ],
     "testPathIgnorePatterns": [
       "/fixtures/",
       "/test-utils/",
@@ -91,5 +94,8 @@
       "/wcag/",
       "/acceptance/"
     ]
+  },
+  "dependencies": {
+    "escape-string-regexp": "^5.0.0"
   }
 }

static/js/is-staging.js

@@ -1,9 +1,20 @@
+import escapeStringRegexp from 'escape-string-regexp';
+
 /**
  * Determines whether the current url is staging or production.
  */
 export function isStaging(stagingDomains) {
   const defaultStagingDomains = ['127.0.0.1', 'localhost', 'office.yext.com'];
-  const _stagingDomains = defaultStagingDomains.concat(stagingDomains);
-  const currentUrl = window.location.href;
-  return _stagingDomains.some(domain => currentUrl.includes(domain));
+  const _stagingDomains = stagingDomains
+    ? defaultStagingDomains.concat(stagingDomains)
+    : defaultStagingDomains;
+  const currentDomain = window.location.hostname;
+
+  return _stagingDomains.some(domain => {
+    const regexEscapedDomain = escapeStringRegexp(domain);
+    // The RFC for subdomains says they can contain a maximum of 63 characters. The leading and trailing characters must be alpha numeric. 
+    const isSubdomainRegex = new RegExp(`[A-Za-z0-9]?[A-Za-z0-9\-]{0,61}[A-Za-z0-9]?\.${regexEscapedDomain}`);
+
+    return domain === currentDomain || isSubdomainRegex.test(currentDomain);
+  });
 }