doc: replace function expressions with arrows

This commit replaces multiple usages of `function(){}` with ES2015
arrow functions in places it was forgotten earlier. The goal is to
make the docs more consistent since other functions were already
replaced with ES2015 arrows.

In addition, it fixes invalid syntax in modules.markdown to valid
syntax as well as remove `var self = this` pattern usages in the code
where they are now possible to avoid through arrow functions.

PR-URL: #4832
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/addons.markdown

@@ -44,7 +44,9 @@ be used as a starting-point for your own Addon.
 This "Hello world" example is a simple Addon, written in C++, that is the
 equivalent of the following JavaScript code:
 
-    module.exports.hello = function() { return 'world'; };
+```js
+module.exports.hello = () => 'world';
+```
 
 First, create the file `hello.cc`:
 
@@ -368,7 +370,7 @@ To test it, run the following JavaScript:
 // test.js
 const addon = require('./build/Release/addon');
 
-addon(function(msg){
+addon((msg) => {
   console.log(msg); // 'hello world'
 });
 ```

doc/api/assert.markdown

@@ -139,7 +139,7 @@ matching error type in the assertion:
 
 ```js
 assert.doesNotThrow(
-  function() {
+  () => {
     throw new TypeError('Wrong value');
   },
   SyntaxError
@@ -151,7 +151,7 @@ However, the following will result in an `AssertionError` with the message
 
 ```js
 assert.doesNotThrow(
-  function() {
+  () => {
     throw new TypeError('Wrong value');
   },
   TypeError
@@ -164,7 +164,7 @@ message:
 
 ```js
 assert.doesNotThrow(
-  function() {
+  () => {
     throw new TypeError('Wrong value');
   },
   TypeError,
@@ -359,7 +359,7 @@ Validate instanceof using constructor:
 
 ```js
 assert.throws(
-  function() {
+  () => {
     throw new Error('Wrong value');
   },
   Error
@@ -370,7 +370,7 @@ Validate error message using [`RegExp`][]:
 
 ```js
 assert.throws(
-  function() {
+  () => {
     throw new Error('Wrong value');
   },
   /value/
@@ -381,7 +381,7 @@ Custom error validation:
 
 ```js
 assert.throws(
-  function() {
+  () => {
     throw new Error('Wrong value');
   },
   function(err) {

doc/api/debugger.markdown

@@ -15,7 +15,7 @@ debug; a prompt will be displayed indicating successful launch of the debugger:
 connecting... ok
 break in /home/indutny/Code/git/indutny/myscript.js:1
   1 x = 5;
-  2 setTimeout(function () {
+  2 setTimeout(() => {
   3   debugger;
 debug>
 ```
@@ -31,7 +31,7 @@ For example, suppose `myscript.js` is written as:
 ```js
 // myscript.js
 x = 5;
-setTimeout(function () {
+setTimeout(() => {
   debugger;
   console.log('world');
 }, 1000);
@@ -46,19 +46,19 @@ Once the debugger is run, a breakpoint will occur at line 4:
 connecting... ok
 break in /home/indutny/Code/git/indutny/myscript.js:1
   1 x = 5;
-  2 setTimeout(function () {
+  2 setTimeout(() => {
   3   debugger;
 debug> cont
 < hello
 break in /home/indutny/Code/git/indutny/myscript.js:3
   1 x = 5;
-  2 setTimeout(function () {
+  2 setTimeout(() => {
   3   debugger;
   4   console.log('world');
   5 }, 1000);
 debug> next
 break in /home/indutny/Code/git/indutny/myscript.js:4
-  2 setTimeout(function () {
+  2 setTimeout(() => {
   3   debugger;
   4   console.log('world');
   5 }, 1000);
@@ -136,7 +136,7 @@ Warning: script 'mod.js' was not loaded yet.
 debug> c
 break in test/fixtures/break-in-module/mod.js:23
  21
- 22 exports.hello = function() {
+ 22 exports.hello = () => {
  23   return 'hello from module';
  24 };
  25

doc/api/domain.markdown

@@ -349,7 +349,7 @@ thrown will be routed to the domain's `'error'` event.
 const d = domain.create();
 
 function readSomeFile(filename, cb) {
-  fs.readFile(filename, 'utf8', d.bind(function(er, data) {
+  fs.readFile(filename, 'utf8', d.bind((er, data) => {
     // if this throws, it will also be passed to the domain
     return cb(er, data ? JSON.parse(data) : null);
   }));
@@ -380,7 +380,7 @@ with a single error handler in a single place.
 const d = domain.create();
 
 function readSomeFile(filename, cb) {
-  fs.readFile(filename, 'utf8', d.intercept(function(data) {
+  fs.readFile(filename, 'utf8', d.intercept((data) => {
     // note, the first argument is never passed to the
     // callback since it is assumed to be the 'Error' argument
     // and thus intercepted by the domain.

doc/api/events.markdown

@@ -37,7 +37,7 @@ function MyEmitter() {
 util.inherits(MyEmitter, EventEmitter);
 
 const myEmitter = new MyEmitter();
-myEmitter.on('event', function() {
+myEmitter.on('event', () => {
   console.log('an event occurred!');
 });
 myEmitter.emit('event');
@@ -54,7 +54,7 @@ const EventEmitter = require('events');
 class MyEmitter extends EventEmitter {}
 
 const myEmitter = new MyEmitter();
-myEmitter.on('event', function() {
+myEmitter.on('event', () => {
   console.log('an event occurred!');
 });
 myEmitter.emit('event');
@@ -364,7 +364,7 @@ Removes the specified `listener` from the listener array for the specified
 `event`.
 
 ```js
-var callback = function(stream) {
+var callback = (stream) => {
   console.log('someone connected!');
 };
 server.on('connection', callback);

doc/api/fs.markdown

@@ -239,7 +239,7 @@ argument will be populated. The following example checks if the file
 `/etc/passwd` can be read and written by the current process.
 
 ```js
-fs.access('/etc/passwd', fs.R_OK | fs.W_OK, function (err) {
+fs.access('/etc/passwd', fs.R_OK | fs.W_OK, (err) => {
   console.log(err ? 'no access!' : 'can read/write');
 });
 ```

doc/api/modules.markdown

@@ -20,13 +20,10 @@ The contents of `circle.js`:
 ```js
 const PI = Math.PI;
 
-exports.area = function (r) {
-  return PI * r * r;
-};
+exports.area = (r) => PI * r * r;
+
+exports.circumference = (r) => 2 * PI * r;
 
-exports.circumference = function (r) {
-  return 2 * PI * r;
-};
 ```
 
 The module `circle.js` has exported the functions `area()` and
@@ -53,11 +50,9 @@ The `square` module is defined in `square.js`:
 
 ```js
 // assigning to exports will not modify module, must use module.exports
-module.exports = function(width) {
+module.exports = (width) => {
   return {
-    area: function() {
-      return width * width;
-    }
+    area: () => width * width
   };
 }
 ```
@@ -498,12 +493,12 @@ To illustrate the behavior, imagine this hypothetical implementation of
 ```js
 function require(...) {
   // ...
-  function (module, exports) {
+  ((module, exports) => {
     // Your module code here
     exports = some_func;        // re-assigns exports, exports is no longer
                                 // a shortcut, and nothing is exported.
     module.exports = some_func; // makes your module export 0
-  } (module, module.exports);
+  })(module, module.exports);
   return module;
 }
 ```

doc/api/process.markdown

@@ -179,7 +179,7 @@ var resource = new SomeResource();
 
 In cases like this, you may not want to track the rejection as a developer
 error like you would for other `'unhandledRejection'` events. To address
-this, you can either attach a dummy `.catch(function() { })` handler to
+this, you can either attach a dummy `.catch(() => { })` handler to
 `resource.loaded`, preventing the `'unhandledRejection'` event from being
 emitted, or you can use the [`'rejectionHandled'`][] event.
 
@@ -750,7 +750,7 @@ function maybeSync(arg, cb) {
 This API is hazardous.  If you do this:
 
 ```js
-maybeSync(true, function() {
+maybeSync(true, () => {
   foo();
 });
 bar();
@@ -986,7 +986,7 @@ A `Writable Stream` to `stdout` (on fd `1`).
 For example, a `console.log` equivalent could look like this:
 
 ```js
-console.log = function(msg) {
+console.log = (msg) => {
   process.stdout.write(`${msg}\n`);
 };
 ```

doc/api/readline.markdown

@@ -266,7 +266,7 @@ const rl = readline.createInterface({
   input: fs.createReadStream('sample.txt')
 });
 
-rl.on('line', function (line) {
+rl.on('line', (line) => {
   console.log('Line from file:', line);
 });
 ```

doc/api/repl.markdown

@@ -15,7 +15,7 @@ mjr:~$ node
 Type '.help' for options.
 > a = [ 1, 2, 3];
 [ 1, 2, 3 ]
-> a.forEach(function (v){
+> a.forEach((v) => {
 ...   console.log(v);
 ...   });
 1
@@ -139,7 +139,7 @@ For example, if you have defined an `inspect()` function on an object, like this
 ```
 > var obj = {foo: 'this will not show up in the inspect() output'};
 undefined
-> obj.inspect = function() {
+> obj.inspect = () => {
 ...   return {bar: 'baz'};
 ... };
 [Function]

doc/api/stream.markdown

@@ -925,18 +925,17 @@ function SourceWrapper(options) {
   Readable.call(this, options);
 
   this._source = getLowlevelSourceObject();
-  var self = this;
 
   // Every time there's data, we push it into the internal buffer.
-  this._source.ondata = function(chunk) {
+  this._source.ondata = (chunk) => {
     // if push() returns false, then we need to stop reading from source
-    if (!self.push(chunk))
-      self._source.readStop();
+    if (!this.push(chunk))
+      this._source.readStop();
   };
 
   // When the source ends, we push the EOF-signaling `null` chunk
-  this._source.onend = function() {
-    self.push(null);
+  this._source.onend = () => {
+    this.push(null);
   };
 }
 

doc/api/util.markdown

@@ -58,7 +58,7 @@ Marks that a method should not be used any more.
 ```js
 const util = require('util');
 
-exports.puts = util.deprecate(function() {
+exports.puts = util.deprecate(() => {
   for (var i = 0, len = arguments.length; i < len; ++i) {
     process.stdout.write(arguments[i] + '\n');
   }

doc/api/zlib.markdown

@@ -29,16 +29,20 @@ the convenience methods.
 
 ```js
 const input = '.................................';
-zlib.deflate(input, function(err, buffer) {
+zlib.deflate(input, (err, buffer) => {
   if (!err) {
     console.log(buffer.toString('base64'));
+  } else {
+    // handle error
   }
 });
 
 const buffer = new Buffer('eJzT0yMAAGTvBe8=', 'base64');
-zlib.unzip(buffer, function(err, buffer) {
+zlib.unzip(buffer, (err, buffer) => {
   if (!err) {
     console.log(buffer.toString());
+  } else {
+    // handle error
   }
 });
 ```