add generateUUID.js

String/generateUUID.js

@@ -0,0 +1,45 @@
+/* Generates a UUID/GUID in Node.Js or browser.
+
+In the browser the script uses the `window.crypto` or `window.msCrypto` (IE11) API
+On server-side the script uses `Math.random` in combination with the timestamp for better randomness.
+The function generate an RFC4122 (https://www.ietf.org/rfc/rfc4122.txt) version 4 UUID/GUID
+
+*/
+const Guid = () => {
+  const crypto = typeof window || window.crypto || window.msCrypto || null
+  const pattern = 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'
+
+  const _padLeft = (paddingString, width, replacementChar) =>
+    paddingString.length >= width
+      ? paddingString
+      : _padLeft(replacementChar + paddingString, width, replacementChar || ' ')
+
+  const _quart = number => {
+    const hexadecimalResult = number.toString(16)
+    return _padLeft(hexadecimalResult, 4, '0')
+  }
+  const _cryptoGuid = () => {
+    const buffer = new window.Uint16Array(8)
+    window.crypto.getRandomValues(buffer)
+    return [_quart(buffer[0]) +
+    _quart(buffer[1]), _quart(buffer[2]), _quart(buffer[3]), _quart(buffer[4]), _quart(buffer[5]) +
+    _quart(buffer[6]) +
+    _quart(buffer[7])].join('-')
+  }
+  const _guid = () => {
+    let currentDateMilliseconds = new Date().getTime()
+    return pattern.replace(/[xy]/g, currentChar => {
+      const randomChar = (currentDateMilliseconds + Math.random() * 16) % 16 | 0
+      currentDateMilliseconds = Math.floor(currentDateMilliseconds / 16)
+      return (currentChar === 'x' ? randomChar : (randomChar & 0x7 | 0x8)).toString(16)
+    })
+  }
+
+  return crypto !== 'undefined' && crypto !== null
+    ? typeof (window.crypto.getRandomValues) !== 'undefined'
+      ? _cryptoGuid()
+      : _guid()
+    : _guid()
+}
+
+console.log(Guid()) // 'edc848db-3478-1760-8b55-7986003d895f'