Add singleton package assertion (& add to keyring) (#384)

* Add signleton package assertion (& add to keyring)

* CHANGELOG

* Add test

packages/util/src/assertSingletonPackage.spec.ts

@@ -0,0 +1,21 @@
+// Copyright 2017-2019 @polkadot/util authors & contributors
+// This software may be modified and distributed under the terms
+// of the Apache-2.0 license. See the LICENSE file for details.
+
+import { assertSingletonPackage } from '.';
+
+describe('assertSingletonPackage', () => {
+  const NAME = 'assertSingletonPackage';
+
+  it('should not throw the first time', () => {
+    expect(
+      () => assertSingletonPackage(NAME)
+    ).not.toThrow();
+  });
+
+  it('should throw the second time', () => {
+    expect(
+      () => assertSingletonPackage(NAME)
+    ).toThrow(/Multiple versions of assertSingletonPackage detected/);
+  });
+});

packages/util/src/assertSingletonPackage.ts

@@ -0,0 +1,22 @@
+// Copyright 2017-2019 @polkadot/util authors & contributors
+// This software may be modified and distributed under the terms
+// of the Apache-2.0 license. See the LICENSE file for details.
+
+import isUndefined from './is/undefined';
+import assert from './assert';
+
+/**
+ * @name assertSingletonPackage
+ * @summary Checks that a specific package is only imported once
+ */
+export default function assertSingletonPackage (name: string): void {
+  const _global: any = isUndefined(window) ? global : window;
+
+  if (isUndefined(_global.__polkadotjs)) {
+    _global.__polkadotjs = {};
+  }
+
+  assert(isUndefined(_global.__polkadotjs[name]), `Multiple versions of ${name} detected, ensure that there is only version one in your dependency tree`);
+
+  _global.__polkadotjs[name] = true;
+}

packages/util/src/index.ts

@@ -9,6 +9,7 @@ import './polyfill';
  */
 
 export { default as assert } from './assert';
+export { default as assertSingletonPackage } from './assertSingletonPackage';
 export { default as logger } from './logger';
 export { default as promisify } from './promisify';