Add ability to run Webpack in series (#44)

* Add ability to run webpack in series

* Use console.log instead of sls.cli.log

* Fix ESLint errors

* Reduce webpack configurations with ramda

README.md

@@ -38,6 +38,7 @@ By default the plugin will look for a `webpack.config.js` in the service root. Y
 custom:
   webpack:
     config: ./path/to/config/file.js
+    series: true # run Webpack in series, useful for large projects. Defaults to false.
 ```
 
 The `entry` and `output` objects are set by the plugin.

src/index.js

@@ -55,8 +55,10 @@ class ServerlessPluginWebpack {
     // Include bundle at function level
     this.serverless.service.functions = service.setFnsPackage(this.serverless.service.functions);
 
+    const runWebpack = this.custom.series ? wpack.runSeries : wpack.run;
+
     // Run webpack
-    return wpack.run(wpack.createConfigs(
+    return runWebpack(wpack.createConfigs(
       this.originalFunctions,
       webpackConfig,
       this.originalServicePath,

src/lib/wpack.js

@@ -76,7 +76,13 @@ const run = configs =>
     });
   });
 
+/**
+ * Runs webpack with an array of configurations in series
+ */
+const runSeries = R.reduce((promise, config) => promise.then(() => run(config)), Promise.resolve());
+
 module.exports = {
   createConfigs,
   run,
+  runSeries,
 };