refactor(isExternal): avoid undefined & improve performance

lib/is_external_link.js

@@ -1,34 +1,28 @@
 'use strict';
 
-const { URL } = require('url');
-
-const urlObj = (str) => {
-  try {
-    return new URL(str);
-  } catch (err) {
-    return str;
-  }
-};
+const { parse, URL } = require('url');
 
 /**
  * Check whether the link is external
- * @param {String} url The url to check
+ * @param {String} input The url to check
  * @returns {Boolean} True if the link doesn't have protocol or link has same host with config.url
  */
 
-function isExternalLink(url) {
+function isExternalLink(input) {
   const { config } = this;
-  const exclude = Array.isArray(config.external_link.exclude) ? config.external_link.exclude
-    : [config.external_link.exclude];
-  const data = urlObj(url);
-  const host = data.hostname;
-  const sitehost = typeof urlObj(config.url) === 'object' ? urlObj(config.url).hostname : config.url;
+  const sitehost = parse(config.url).hostname || config.url;
+  if (!sitehost) return false;
 
-  if (!sitehost || typeof data === 'string') return false;
+  // handle relative url
+  const data = new URL(input, `http://${sitehost}`);
 
   // handle mailto: javascript: vbscript: and so on
   if (data.origin === 'null') return false;
 
+  const host = data.hostname;
+  const exclude = Array.isArray(config.external_link.exclude) ? config.external_link.exclude
+    : [config.external_link.exclude];
+
   if (exclude && exclude.length) {
     for (const i of exclude) {
       if (host === i) return false;