Remove dependencies on yarn

.travis.yml

@@ -56,7 +56,6 @@ matrix:
         jwt:
           secure: "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"
 cache:
-  yarn: true
   directories:
   - node_modules
   - .gem

build-system/SERVING.md

@@ -21,15 +21,14 @@ limitations under the License.
 - node + npm
 - gulp (installed globally)
 - java 8
-- yarn (see https://yarnpkg.com/)
 
 ## Steps
 ```bash
 git clone https://github.com/ampproject/amphtml.git
 cd amphtml
 # Checkout a tag
 git checkout 123456789
-yarn
+npm install
 gulp clean
 # We only need to build the css files, no need to generate `max` files
 gulp build --css-only

build-system/pr-check.js

@@ -380,17 +380,17 @@ function main(argv) {
     process.exit(1);
   }
 
-  // Make sure changes to package.json also update yarn.lock.
-  if (files.indexOf('package.json') != -1 && files.indexOf('yarn.lock') == -1) {
+  // Make sure changes to package.json also update package-lock.json.
+  if (files.indexOf('package.json') != -1 && files.indexOf('package-lock.json') == -1) {
     console.error(fileLogPrefix, util.colors.red('ERROR:'),
         'Updates to', util.colors.cyan('package.json'),
         'must be accompanied by a corresponding update to',
-        util.colors.cyan('yarn.lock'));
+        util.colors.cyan('package-lock.json'));
     console.error(fileLogPrefix, util.colors.yellow('NOTE:'),
-        'To update', util.colors.cyan('yarn.lock'), 'after changing',
+        'To update', util.colors.cyan('package-lock.json'), 'after changing',
         util.colors.cyan('package.json') + ',', 'run',
-        '"' + util.colors.cyan('yarn install') + '"',
-        'and include the change to', util.colors.cyan('yarn.lock'),
+        '"' + util.colors.cyan('npm purge && npm install') + '"',
+        'and include the change to', util.colors.cyan('package-lock.json'),
         'in your PR.');
     process.exit(1);
   }

contributing/DEVELOPING.md

@@ -30,7 +30,7 @@ Before you start developing in AMP, check out these resources:
 
 For most developers the instructions in the [Getting Started Quick Start Guide](getting-started-quick.md) will be sufficient for building/running/testing during development.  This section provides a more detailed reference.
 
-The Quick Start Guide's  [One-time setup](getting-started-quick.md#one-time-setup) has instructions for installing Node.js, Yarn, and Gulp which you'll need before running these commands.
+The Quick Start Guide's  [One-time setup](getting-started-quick.md#one-time-setup) has instructions for installing Node.js, npm, and Gulp which you'll need before running these commands.
 
 | Command                                                                 | Description                                                           |
 | ----------------------------------------------------------------------- | --------------------------------------------------------------------- |

contributing/getting-started-e2e.md

@@ -151,16 +151,17 @@ Now run `git remote -v` again and notice that you have set up your upstream alia
 
 Now that you have all of the files copied locally you can actually build the code and run a local server to try things out.
 
-amphtml uses Node.js, the yarn package manager and the Gulp build system to build amphtml and start up a local server that lets you try out your changes.  Installing these and getting amphtml built is straightforward:
+amphtml uses Node.js, the npm package manager and the Gulp build system to build amphtml and start up a local server that lets you try out your changes.  Installing these and getting amphtml built is straightforward:
 
-* Install [NodeJS](https://nodejs.org/) (which includes npm).
+* Install [NodeJS](https://nodejs.org/) version >= 4.7 (which includes npm)
 
-* Install [yarn](https://yarnpkg.com/en/docs/install)
+* Install [npm](https://www.npmjs.com/get-npm) version >= 5
 
 * In your local repository directory (e.g. `~/src/ampproject/amphtml`), install the packages that AMP uses by running
    ```
-   yarn
+   npm install
    ```
+
    You should see a progress indicator and some messages scrolling by.  You may see some warnings about optional dependencies that are generally safe to ignore.
 
 * For some local testing we refer to fake local URLs in order to simulate referencing third party URLs.  This requires extra setup so your browser will know that these URLs actually point to your local server.
@@ -171,12 +172,14 @@ amphtml uses Node.js, the yarn package manager and the Gulp build system to buil
 
 * The AMP Project uses Gulp as our build system.   Gulp uses a configuration file ([gulpfile.js](https://github.com/ampproject/amphtml/blob/master/gulpfile.js)) to build amphtml (including the amphtml javascript) and to start up the Node.js server with the proper settings.  You don't really have to understand exactly what it is doing at this point--you just have to install it and use it.
 
-   You can install Gulp using yarn:
+   You can install Gulp using npm:
 
    ```
-   yarn global add gulp
+   npm install -g gulp
    ```
 
+   On some platform the preceding command might require elevated privileges using `sudo`.
+
 Now whenever you're ready to build amphtml and start up your local server, simply go to your local repository directory and run:
 
 ```

contributing/getting-started-quick.md

@@ -25,11 +25,11 @@ This Quick Start guide is the TL;DR version of the longer [end-to-end guide](get
 
 * [Install and set up Git](https://help.github.com/articles/set-up-git/); in the "Authenticating" step of that page use SSH instead of HTTPS
 
-* Install [NodeJS](https://nodejs.org/)
+* Install [NodeJS](https://nodejs.org/) version >= 4.7
 
-* Install [yarn](https://yarnpkg.com/en/docs/install)
+* Install [npm](https://www.npmjs.com/get-npm)` version >= 5
 
-* Install Gulp by running `yarn global add gulp`
+* Install Gulp by running `npm install -g gulp` (on some platforms this command might require elevated privileges using `sudo`)
 
 * Add this line to your hosts file (`/etc/hosts` on Mac or Linux, `%SystemRoot%\System32\drivers\etc\hosts` on Windows):
 
@@ -48,7 +48,7 @@ This Quick Start guide is the TL;DR version of the longer [end-to-end guide](get
 * Go to the branch: `git checkout <branch name>`
 
 # Build AMP & run a local server
-* Make sure you have the latest packages (after you pull): `yarn`
+* Make sure you have the latest packages (after you pull): `npm install`
 * Start the server: `gulp`
 * Access your server at [http://localhost:8000](http://localhost:8000)
 * Access your sample pages at [http://localhost:8000/examples](http://localhost:8000/examples)
@@ -62,6 +62,7 @@ This Quick Start guide is the TL;DR version of the longer [end-to-end guide](get
 # Create commits to contain your changes
 
 * Edit files in your favorite editor
+* If you edited `package.json` run `npm prune && npm install` to generate an updated `package-lock.json` file
 * Add each file you change: `git add <file>`
 * Create a commit: `git commit -m "<your commit message>"`
 * Instead of `add`ing each file individually you can use the `-a` flag on the commit instead