Merge pull request #249 from ckeditor/t/ckeditor5/1005

Feature: Implemented a module exposing the `CKEDIOR_VERSION` to the global scope. Closes ckeditor/ckeditor5#1005.

package.json

@@ -8,6 +8,9 @@
     "ckeditor 5",
     "ckeditor5-lib"
   ],
+  "dependencies": {
+    "ckeditor5": "^10.1.0"
+  },
   "devDependencies": {
     "@ckeditor/ckeditor5-core": "^10.1.0",
     "@ckeditor/ckeditor5-engine": "^10.1.0",

src/version.js

@@ -0,0 +1,57 @@
+/**
+ * @license Copyright (c) 2003-2018, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md.
+ */
+
+/**
+ * @module utils/version
+ */
+
+/* globals window, global */
+
+import log from './log';
+import { version } from 'ckeditor5/package.json';
+
+const windowOrGlobal = typeof window === 'object' ? window : global;
+
+if ( windowOrGlobal.CKEDITOR_VERSION ) {
+	/**
+	 * This error is thrown when the `CKEDITOR_VERSION` global is being set more than once. This happens when in
+	 * two scenarios described above.
+	 *
+	 * # Some packages were duplicated
+	 *
+	 * CKEditor 5 was built from source packages which were duplicated during installation via npm.
+	 * Normally, npm deduplicates all packages so e.g. `@ckeditor/ckeditor5-core` is installed only once in `node_modules/`.
+	 * However, subsequent `npm install` calls or conflicting version dependencies may cause npm to install some packages
+	 * more than once. Furthermore, [npm in version 5+](https://github.com/npm/npm/issues/16991)
+	 * is also known for randomly failing to deduplicate packages.
+	 *
+	 * We recommend checking if any of the below steps helps:
+	 *
+	 * * `rm -rf node_modules && npm install` to make sure you have a clean `node_modules/` – this step
+	 * is known to help in majority of cases,
+	 * * check whether all CKEditor 5 packages are up to date and reinstall them
+	 * if you changed anything (`rm -rf node_modules && npm install`),
+	 * * downgrade npm to version 4 if you use a newer version.
+	 *
+	 * If all packages are correct and compatible with each other the above steps are known to help. If not, you may
+	 * try to check with `npm ls` how many times `@ckeditor/ckeditor5-core` is installed. If more than once, verify
+	 * which package causes that.
+	 *
+	 * # Two+ builds are loaded
+	 *
+	 * If you use CKEditor 5 builds, you might have loaded two (or more) `ckeditor.js` files in one web page
+	 * – check your web page for duplicated `<script>` elements or make sure your page builder/bundler includes CKEditor only once.
+	 *
+	 * @error ckeditor-version-collision
+	 * @param {String} collidingVersion The version of the build which has already been (incorrectly) loaded.
+	 * @param {String} version The version of the build which is supposed to be loaded.
+	 */
+	log.error( 'ckeditor-version-collision: The global CKEDITOR_VERSION constant has already been set.', {
+		collidingVersion: windowOrGlobal.CKEDITOR_VERSION,
+		version
+	} );
+} else {
+	windowOrGlobal.CKEDITOR_VERSION = version;
+}