tools: make doc tool a bit more readable

PR-URL: https://github.com/nodejs/node/pull/17125
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

tools/doc/generate.js

@@ -30,13 +30,13 @@ const fs = require('fs');
 const args = process.argv.slice(2);
 let format = 'json';
 let template = null;
-let inputFile = null;
+let filename = null;
 let nodeVersion = null;
 let analytics = null;
 
 args.forEach(function(arg) {
   if (!arg.startsWith('--')) {
-    inputFile = arg;
+    filename = arg;
   } else if (arg.startsWith('--format=')) {
     format = arg.replace(/^--format=/, '');
   } else if (arg.startsWith('--template=')) {
@@ -50,41 +50,32 @@ args.forEach(function(arg) {
 
 nodeVersion = nodeVersion || process.version;
 
-if (!inputFile) {
+if (!filename) {
   throw new Error('No input file specified');
 }
 
-fs.readFile(inputFile, 'utf8', function(er, input) {
+fs.readFile(filename, 'utf8', (er, input) => {
   if (er) throw er;
   // process the input for @include lines
-  processIncludes(inputFile, input, next);
+  processIncludes(filename, input, next);
 });
 
 function next(er, input) {
   if (er) throw er;
   switch (format) {
     case 'json':
-      require('./json.js')(input, inputFile, function(er, obj) {
+      require('./json.js')(input, filename, (er, obj) => {
         console.log(JSON.stringify(obj, null, 2));
         if (er) throw er;
       });
       break;
 
     case 'html':
-      require('./html.js')(
-        {
-          input: input,
-          filename: inputFile,
-          template: template,
-          nodeVersion: nodeVersion,
-          analytics: analytics,
-        },
-
-        function(er, html) {
-          if (er) throw er;
-          console.log(html);
-        }
-      );
+      require('./html')({ input, filename, template, nodeVersion, analytics },
+                        (err, html) => {
+                          if (err) throw err;
+                          console.log(html);
+                        });
       break;
 
     default:

tools/doc/html.js

@@ -125,9 +125,7 @@ function toID(filename) {
  * opts: lexed, filename, template, nodeVersion.
  */
 function render(opts, cb) {
-  var lexed = opts.lexed;
-  var filename = opts.filename;
-  var template = opts.template;
+  var { lexed, filename, template } = opts;
   const nodeVersion = opts.nodeVersion || process.version;
 
   // get the section