Add .nvmrc file (#17145) (#17174)

* Add .nvmrc file

* Update contributing docs

* Fix typo in `nvm use`

* Update "install node" text

* Add test to ensure .nvmrc and .node-version are identical

* Use async/await instead of promise

* Feedback

.nvmrc

@@ -0,0 +1 @@
+8.9.4

CONTRIBUTING.md

@@ -152,10 +152,10 @@ git clone https://github.com/[YOUR_USERNAME]/kibana.git kibana
 cd kibana
 ```
 
-Install the version of node.js listed in the `.node-version` file _(this can be easily automated with tools such as [nvm](https://github.com/creationix/nvm) and [avn](https://github.com/wbyoung/avn))_
+Install the version of Node.js listed in the `.node-version` file. This can be automated with tools such as [nvm](https://github.com/creationix/nvm), [nvm-windows](https://github.com/coreybutler/nvm-windows) or [avn](https://github.com/wbyoung/avn). As we also include a `.nvmrc` file you can switch to the correct version when using nvm by running:
 
 ```bash
-nvm install "$(cat .node-version)"
+nvm use
 ```
 
 Install the latest version of [yarn](https://yarnpkg.com).

src/dev/__tests__/node_versions_must_match.js

@@ -0,0 +1,23 @@
+import fs from 'fs';
+import { engines } from '../../../package.json';
+import { promisify } from 'util';
+const readFile = promisify(fs.readFile);
+import expect from 'expect.js';
+
+describe('All configs should use a single version of Node', () => {
+  it('should compare .node-version and .nvmrc', async () => {
+    const [nodeVersion, nvmrc] = await Promise.all([
+      readFile('./.node-version', { encoding: 'utf-8' }),
+      readFile('./.nvmrc', { encoding: 'utf-8' }),
+    ]);
+
+    expect(nodeVersion.trim()).to.be(nvmrc.trim());
+  });
+
+  it('should compare .node-version and engines.node from package.json', async () => {
+    const nodeVersion = await readFile('./.node-version', {
+      encoding: 'utf-8',
+    });
+    expect(nodeVersion.trim()).to.be(engines.node);
+  });
+});