Improve, Refactor: Add some notes

src/index.ts

@@ -1,26 +1,41 @@
+/**
+ * summaly
+ * https://github.com/syuilo/summaly
+ */
+
 import * as URL from 'url';
 import tracer from 'trace-redirect';
 import ISummary from './isummary';
 import IPlugin from './iplugin';
 import general from './general';
 
+// Load plugins
 const plugins: IPlugin[] = require('require-all')({
 	dirname: __dirname + '/plugins'
 });
 
+/**
+ * Summary an web page
+ * @param  {string}            url URL of web page you want to summary
+ * @return {Promise<ISummary>}     Promised summary
+ */
 export default async (url: string): Promise<ISummary> => {
+	// Follow redirects
 	const actualUrl = await tracer(url);
 
 	const _url = URL.parse(actualUrl, true);
 
+	// Find matching plugin
 	const match = Object.keys(plugins)
 		.map(key => plugins[key])
 		.filter(plugin => plugin.test(_url))[0] as IPlugin;
 
+	// Get summary
 	const summary = match
 		? await match.summary(_url)
 		: await general(_url);
 
+	// Replace '' to null
 	Object.keys(summary).forEach(k => {
 		if (summary[k]) {
 			summary[k] = summary[k].trim();