Add URLJoin.md

snippets/URLJoin.md

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+### URLJoin
+
+Joins all given URL segments together, then normalizes the resulting URL.
+
+Use `String.join('/')` to combine URL segments, then a series of `String.replace()` calls with various regexps to normalize the resulting URL (remove double slashes, add proper slashes for protocol, remove slashes before parameters, combine parameters with `'&'` and normalize first parameter delimiter).
+
+```js
+const URLJoin = (...args) =>
+  args.join('/')
+  .replace(/[\/]+/g,'/')
+  .replace(/^(.+):\//,'$1://')
+  .replace(/^file:/,'file:/')
+  .replace(/\/(\?|&|#[^!])/g, '$1')
+  .replace(/\?/g,'&')
+  .replace('&','?');
+```
+
+```js
+URLJoin('http://www.google.com', 'a', '/b/cd', '?foo=123', '?bar=foo'); // 'http://www.google.com/a/b/cd?foo=123&bar=foo'
+```