JavaScript: The Good Parts

Category: Programming
Author: Douglas Crockford
All Stack Overflow 137
This Year Stack Overflow 2
This Month Stack Overflow 1


by solidist   2020-07-04
JavaScript: The Good Parts by Douglas Crockford. Note that this was written in 2008 but still holds up well.

It may be a perfect time for a revision.

by no_wizard   2020-06-19
I also want to add the great Eloquent JavaScript[0] to this list. While its targeted at learning programming as a whole, its still a wonderful resource, even for seasoned programmers, to learn some ins and outs of the language if you haven't had a lot of experience with it.

I also want to give mention to JavaScript: The Good Parts by Douglas Crockford[1], and his new book, How JavaScript Workers[2]



by anonymous   2019-07-21

I watched this Google talk a few weeks ago and was inspired to read Crockford's entire book, "JavaScript: The Good Parts". Watch the talk and I think you'll find it's exactly what you're looking for, full of best practices for using closures & prototype. It's a little old and just covers core JavaScript, nothing about JQuery, ect. but if that's what you're looking for, this is your book.

by anonymous   2019-07-21

OOP with JavaScript is a bit different. Like you, I'm relatively new to this topic so I have been trying to teach myself over the past couple of months. I would recommend reading over some of the articles posted by the other users as well as some of these:


You didn't really specify what exactly you wanted to do with OOP in terms of code, so I can't really provide specific code, but I highly recommend reading these articles and others that you find on the web to get a general idea of what JavaScript is like, how it works with the DOM, and how it is related to OOP.

I hope this helps.


by anonymous   2019-07-21

This code is an example of using introspection to conditionally execute the code. if ( will return truthy if input is an Array (and has a map function) and will return falsy in all other cases.

This code is therefore testing to see whether input is an Array and if not, it is treating it as a number, otherwise it is treating it as an Array.

You can see the definition of the map function on MDN

Best book to learn about JavaScript is "JavaScript the Good Parts"

by anonymous   2019-07-21


I use a notation for inheritance that is based on ExtJS 3, which I find works pretty close to emulating classical inheritance in Java. It basically runs as follows:

// Create an 'Animal' class by extending
// the 'Object' class with our magic method
var Animal = Object.extend(Object, {
    move : function() {alert('moving...');}

// Create a 'Dog' class that extends 'Animal'
var Dog = Object.extend(Animal, {
    bark : function() {alert('woof');}

// Instantiate Lassie
var lassie = new Dog();

// She can move and bark!


I also agree with Eric Miraglia on sticking to namespaces so the code above should be run within its own context outside the window object, this is critical if you intend your code to run as one of many concurrent frameworks / libraries executing in the browser window.

This means that the only way to the window object is via your own namespace / module object:

// Create a namespace / module for your project
window.MyModule = {};

// Commence scope to prevent littering 
// the window object with unwanted variables
(function() {

    var Animal = window.MyModule.Animal = Object.extend(Object, {
         move: function() {alert('moving...');}

    // .. more code



You can also make use of more advances OOP constructs such as interfaces to enhance your application design. My approach to these is to enhance the Function.prototype in order to get a notation along these lines:

var Dog = Object.extend(Animal, {
     bark: function() {
     // more methods ..
}).implement(Mammal, Carnivore);

OO Patterns

As for 'Patterns' in the Java sense, I've only found use for the Singleton pattern (great for caching) and the Observer pattern for event-driven functionality such as assigning some actions when a user clicks on a button.

An example of utilising the Observer Pattern would be:

// Instantiate object
var lassie = new Animal('Lassie');

// Register listener
lassie.on('eat', function(food) { += food;

// Feed lassie by triggering listener
$('#feeding-button').click(function() {
    var food = prompt('How many food units should we give lassie?');
    lassie.trigger('eat', [food]);
    alert('Lassie has already eaten ' + + ' units');

And thats just a couple of tricks in my bag of OO JS, hope they are useful to you.

I recommend if you intend to go down this road that you read Douglas Crockfords Javascript: the Good Parts. Its a brilliant book for this stuff.

by anonymous   2019-07-21

I own David Flanagan's Most Excellent "Javascript: The Definitive Guide" and I agree - it's a must-have for any Javascript developer.

... however ...

The one framework Flanagan covers is jQuery (not Javascript).

I'd recommend the on-line IBM Redbooks for Dojo and JSON:





Etc. etc

And, even more than Flanagan ("The Rhino Book"), I'd very strongly recommend Douglas Crockford's "Javascript: The Good Parts" as a must-have for every Javascript developer:

by anonymous   2019-07-21

This talk was really helpful when I got into different object patterns in javascript. Example code is included in the second link (the video introduces it).

Of course, you should also definitely read


by anonymous   2019-01-13

You should check out a great book on JavaScript by Douglas Crockford. It provides a very good explanation of some of the design decisions taken by JavaScript creators.

One of the important design aspects of JavaScript is its prototypal inheritance system. Objects are first class citizens in JavaScript, so much that regular functions are also implemented as objects ('Function' object to be precise). In my opinion, when it was originally designed to run inside a browser, it was meant to be used to create lots of singleton objects. In browser DOM, you find that window, document etc all singleton objects. Also, JavaScript is loosely typed dynamic language (as opposed to say Python which is strongly typed, dynamic language), as a result, a concept of object extension was implemented through the use of 'prototype' property.

So I think there are some pros for prototype-based OO as implemented in JavaScript:

  1. Suitable in loosely typed environments, no need to define explicit types.
  2. Makes it incredibly easy to implement singleton pattern (compare JavaScript and Java in this regard, and you'll know what I am talking about).
  3. Provides ways of applying a method of an object in the context of a different object, adding and replacing methods dynamically from an object etc. (things which are not possible in a strongly typed languages).

Here are some of the cons of prototypal OO:

  1. No easy way of implementing private variables. Its possible to implement private vars using Crockford's wizardry using closures, but its definitely not as trivial as using private variables in say Java or C#.
  2. I don't know how to implement multiple inheritances (for what its worth) in JavaScript yet.
by anonymous   2018-03-19

So in other words, JSLint doesn't automatically expect me to use a constructor pattern?

You know, I think you're right. Your question bugged me, and I signed up for Crockford's JSLint discussion group and asked. He replied, but ignored the solution I'm going to present, below, which I think means that it's okay, the same way JSLint doesn't complain if something passes muster.

(I'm still waiting for an updated Good Parts, though.)

That caveat aside, here's what I'd suggest doing for OO JavaScript that passes Beta JSLint (as of today, anyhow).

I'm going to rewrite an example from MDN's page, "Introduction to Object Oriented Programming," which itself uses this liberally.

With this

Here's the original, unlinted MDN example from the section linked, above:

var Person = function (firstName) {
  this.firstName = firstName;

Person.prototype.sayHello = function() {
  console.log("Hello, I'm " + this.firstName);

var person1 = new Person("Alice");
var person2 = new Person("Bob");

// call the Person sayHello method.
person1.sayHello(); // logs "Hello, I'm Alice"
person2.sayHello(); // logs "Hello, I'm Bob"

That follows the conventions we know and love.

Without this

It's pretty easy to figure out how to make "constructors" that don't follow that pattern, but we lose use of prototype, if I'm not missing something, and have to include all of the object's methods in our constructor that we want all of our Peeps to share.

/*jslint white:true, devel:true */
var Peep = function(firstName) {
    "use strict";
    var peep = {};
    peep.firstName = firstName;

    peep.innerSayHello = function() {
        console.log("Hello, I'm " + peep.firstName + ".");

    return peep;

var peep1 = new Peep("Bob");
var peep2 = new Peep("Doug");


So there's a lintable alternative. That does, other than the return peep; and the inner definition of methods, make JavaScript act like many OO-first languages you might encounter. It's not wrong, at least.

Not having access to prototype isn't horrible; it's really bad news to change prototype somewhere that's not right beside the constructor, as your code would go to spaghetti. "Some Persons have sayGoodbye() and some don't, depending on if we'd amended the prototype at the point of their construction." That's awful. So this alternative convention has its advantages.

You can still, of course, add functions to a single instantiation of Peep later, but I'm not sure how you'd access firstName without using this, so perhaps he wants us to stop munging objects after construction.

person1.sayGoodbye = function (other) { 
    console.log("Goodbye, " + other + "."); 

(I mean, we could also still monkey-patch Peep to change it mid-process, but that's horrible, stupid programming. Usually.)

Inheritance (without this)

And inheritance is easy enough, I think.

var PeepWithGoodbye = function (firstName) {
    "use strict";
    var peepWithGoodbye = new Peep(firstName);

    peepWithGoodbye.innerSayGoodbye = function (otherPeep) {
        if (undefined === otherPeep) {
            otherPeep = { firstName: "you" };
        console.log("This is " + firstName 
            + " saying goodbye to " + otherPeep.firstName + ".");

    return peepWithGoodbye;

var pwg1 = new PeepWithGoodbye("Fred");
pwg1.innerSayHello();           // Hello, I'm Fred.
pwg1.innerSayGoodbye(peep1);    // This is Fred saying goodbye to Bob.
pwg1.innerSayGoodbye();         // This is Fred saying goodbye to you.

EDIT: See also this answer where the asker later found Crockford's suggested means of creating OO javascript. I'm trying to convince that guy to delete that Q&A and move the A here. If he doesn't, I'll probably add his stuff and community wiki it here.

EDIT: See this from MDN for why it works:

(Normally constructors don't return a value, but they can choose to do so if they want to override the normal object creation process.)

by JesDaw   2018-03-19

JavaScript interpreters do something called "semicolon insertion", so if a line without a semicolon is valid, a semicolon will quietly be added to the end of the statement and no error will occur.

var foo = 'bar'
// Valid, foo now contains 'bar'
var bas =
    { prop: 'yay!' }
// Valid, bas now contains object with property 'prop' containing 'yay!'
var zeb =
switch (zeb) {
// Invalid, because the lines following 'var zeb =' aren't an assignable value

Not too complicated and at least an error gets thrown when something is clearly not right. But there are cases where an error is not thrown, but the statements are not executed as intended due to semicolon insertion. Consider a function that is supposed to return an object:

return {
    prop: 'yay!'
// The object literal gets returned as expected and all is well
    prop: 'nay!'
// Oops! return by itself is a perfectly valid statement, so a semicolon
// is inserted and undefined is unexpectedly returned, rather than the object
// literal. Note that no error occurred.

Bugs like this can be maddeningly difficult to hunt down and while you can't ensure this never happens (since there's no way I know of to turn off semicolon insertion), these sorts of bugs are easier to identify when you make your intentions clear by consistently using semicolons. That and explicitly adding semicolons is generally considered good style.

I was first made aware of this insidious little possibility when reading Douglas Crockford's superb and succinct book "JavaScript: The Good Parts". I highly recommend it.

by drallison   2018-01-29
Counterpoint to Doug Crockford, JavaScript: The Good Parts.

Buried inside JavaScript is a nice small language. And then there is the rest.

by anonymous   2017-08-20

Similar to GaborSch's answer, you could use Doug Crockford's memoizer function, which can be found in Chapter 4 of Javascript: The Good Parts. Using memoization took the calculation time for the first 150 terms of the male and female Hofstadter sequences down to 256 ms as compared to almost 8 seconds without memoization.

var memoizer = function (memo, formula) {
  var recur = function (n) {
    var result = memo[n];
    if (typeof result !== 'number') {
      result = formula(recur, n);
      memo[n] = result;
    return result;
  return recur;

var maleHofstadter = memoizer([0], function (recur, n) {
  return n - femaleHofstadter(recur(n-1));

var femaleHofstadter = memoizer([1], function (recur, n) {
  return n - maleHofstadter(recur(n-1));

var N = 150;
var f = [];
var m = [];
for (var i = 0; i <= N; ++i) {

console.log('F: ' + f.join(','));
console.log('M: ' + m.join(','));
by anonymous   2017-08-20

Some Basic:

  • 24 JavaScript Best Practices for Beginners
  • Douglas Crockford's
  • Seven JavaScript Techniques You Should Be Using Today
  • Basic JavaScript - More
  • JavaScript Examples

Some Advanced:

  • JavaScript Tutorials
  • 30+ Best JavaScript Tutorials You Have To See
  • Advanced JavaScript Tutorials

Discussed On Stackoverflow:

  • Hidden Features of JavaScript?
  • What should every JavaScript programmer know?
  • Others


Still have some problems, Stackoverflow is always here for you

by Bill the Lizard   2017-08-20

The identity (===) operator behaves identically to the equality (==) operator except no type conversion is done, and the types must be the same to be considered equal.

Reference: Javascript Tutorial: Comparison Operators

The == operator will compare for equality after doing any necessary type conversions. The === operator will not do the conversion, so if two values are not the same type === will simply return false. Both are equally quick.

To quote Douglas Crockford's excellent JavaScript: The Good Parts,

JavaScript has two sets of equality operators: === and !==, and their evil twins == and !=. The good ones work the way you would expect. If the two operands are of the same type and have the same value, then === produces true and !== produces false. The evil twins do the right thing when the operands are of the same type, but if they are of different types, they attempt to coerce the values. the rules by which they do that are complicated and unmemorable. These are some of the interesting cases:

'' == '0'           // false
0 == ''             // true
0 == '0'            // true

false == 'false'    // false
false == '0'        // true

false == undefined  // false
false == null       // false
null == undefined   // true

' \t\r\n ' == 0     // true

The lack of transitivity is alarming. My advice is to never use the evil twins. Instead, always use === and !==. All of the comparisons just shown produce false with the === operator.


A good point was brought up by @Casebash in the comments and in @Phillipe Laybaert's answer concerning reference types. For reference types == and === act consistently with one another (except in a special case).

var a = [1,2,3];
var b = [1,2,3];

var c = { x: 1, y: 2 };
var d = { x: 1, y: 2 };

var e = "text";
var f = "te" + "xt";

a == b            // false
a === b           // false

c == d            // false
c === d           // false

e == f            // true
e === f           // true

The special case is when you compare a literal with an object that evaluates to the same literal, due to its toString or valueOf method. For example, consider the comparison of a string literal with a string object created by the String constructor.

"abc" == new String("abc")    // true
"abc" === new String("abc")   // false

Here the == operator is checking the values of the two objects and returning true, but the === is seeing that they're not the same type and returning false. Which one is correct? That really depends on what you're trying to compare. My advice is to bypass the question entirely and just don't use the String constructor to create string objects.


by anonymous   2017-08-20

I use Node.js at work, and find it to be very powerful. Forced to choose one word to describe Node.js, I'd say "interesting" (which is not a purely positive adjective). The community is vibrant and growing. JavaScript, despite its oddities can be a great language to code in. And you will daily rethink your own understanding of "best practice" and the patterns of well-structured code. There's an enormous energy of ideas flowing into Node.js right now, and working in it exposes you to all this thinking - great mental weightlifting.

Node.js in production is definitely possible, but far from the "turn-key" deployment seemingly promised by the documentation. With Node.js v0.6.x, "cluster" has been integrated into the platform, providing one of the essential building blocks, but my "production.js" script is still ~150 lines of logic to handle stuff like creating the log directory, recycling dead workers, etc. For a "serious" production service, you also need to be prepared to throttle incoming connections and do all the stuff that Apache does for PHP. To be fair, Ruby on Rails has this exact problem. It is solved via two complementary mechanisms: 1) Putting Ruby on Rails/Node.js behind a dedicated webserver (written in C and tested to hell and back) like Nginx (or Apache / Lighttd). The webserver can efficiently serve static content, access logging, rewrite URLs, terminate SSL, enforce access rules, and manage multiple sub-services. For requests that hit the actual node service, the webserver proxies the request through. 2) Using a framework like Unicorn that will manage the worker processes, recycle them periodically, etc. I've yet to find a Node.js serving framework that seems fully baked; it may exist, but I haven't found it yet and still use ~150 lines in my hand-rolled "production.js".

Reading frameworks like Express makes it seem like the standard practice is to just serve everything through one jack-of-all-trades Node.js service ... "app.use(express.static(__dirname + '/public'))". For lower-load services and development, that's probably fine. But as soon as you try to put big time load on your service and have it run 24/7, you'll quickly discover the motivations that push big sites to have well baked, hardened C-code like Nginx fronting their site and handling all of the static content requests (...until you set up a CDN, like Amazon CloudFront)). For a somewhat humorous and unabashedly negative take on this, see this guy.

Node.js is also finding more and more non-service uses. Even if you are using something else to serve web content, you might still use Node.js as a build tool, using npm modules to organize your code, Browserify to stitch it into a single asset, and uglify-js to minify it for deployment. For dealing with the web, JavaScript is a perfect impedance match and frequently that makes it the easiest route of attack. For example, if you want to grovel through a bunch of JSON response payloads, you should use my underscore-CLI module, the utility-belt of structured data.

Pros / Cons:

  • Pro: For a server guy, writing JavaScript on the backend has been a "gateway drug" to learning modern UI patterns. I no longer dread writing client code.
  • Pro: Tends to encourage proper error checking (err is returned by virtually all callbacks, nagging the programmer to handle it; also, async.js and other libraries handle the "fail if any of these subtasks fails" paradigm much better than typical synchronous code)
  • Pro: Some interesting and normally hard tasks become trivial - like getting status on tasks in flight, communicating between workers, or sharing cache state
  • Pro: Huge community and tons of great libraries based on a solid package manager (npm)
  • Con: JavaScript has no standard library. You get so used to importing functionality that it feels weird when you use JSON.parse or some other build in method that doesn't require adding an npm module. This means that there are five versions of everything. Even the modules included in the Node.js "core" have five more variants should you be unhappy with the default implementation. This leads to rapid evolution, but also some level of confusion.

Versus a simple one-process-per-request model (LAMP):

  • Pro: Scalable to thousands of active connections. Very fast and very efficient. For a web fleet, this could mean a 10X reduction in the number of boxes required versus PHP or Ruby
  • Pro: Writing parallel patterns is easy. Imagine that you need to fetch three (or N) blobs from Memcached. Do this in PHP ... did you just write code the fetches the first blob, then the second, then the third? Wow, that's slow. There's a special PECL module to fix that specific problem for Memcached, but what if you want to fetch some Memcached data in parallel with your database query? In Node.js, because the paradigm is asynchronous, having a web request do multiple things in parallel is very natural.
  • Con: Asynchronous code is fundamentally more complex than synchronous code, and the up-front learning curve can be hard for developers without a solid understanding of what concurrent execution actually means. Still, it's vastly less difficult than writing any kind of multithreaded code with locking.
  • Con: If a compute-intensive request runs for, for example, 100 ms, it will stall processing of other requests that are being handled in the same Node.js process ... AKA, cooperative-multitasking. This can be mitigated with the Web Workers pattern (spinning off a subprocess to deal with the expensive task). Alternatively, you could use a large number of Node.js workers and only let each one handle a single request concurrently (still fairly efficient because there is no process recycle).
  • Con: Running a production system is MUCH more complicated than a CGI model like Apache + PHP, Perl, Ruby, etc. Unhandled exceptions will bring down the entire process, necessitating logic to restart failed workers (see cluster). Modules with buggy native code can hard-crash the process. Whenever a worker dies, any requests it was handling are dropped, so one buggy API can easily degrade service for other cohosted APIs.

Versus writing a "real" service in Java / C# / C (C? really?)

  • Pro: Doing asynchronous in Node.js is easier than doing thread-safety anywhere else and arguably provides greater benefit. Node.js is by far the least painful asynchronous paradigm I've ever worked in. With good libraries, it is only slightly harder than writing synchronous code.
  • Pro: No multithreading / locking bugs. True, you invest up front in writing more verbose code that expresses a proper asynchronous workflow with no blocking operations. And you need to write some tests and get the thing to work (it is a scripting language and fat fingering variable names is only caught at unit-test time). BUT, once you get it to work, the surface area for heisenbugs -- strange problems that only manifest once in a million runs -- that surface area is just much much lower. The taxes writing Node.js code are heavily front-loaded into the coding phase. Then you tend to end up with stable code.
  • Pro: JavaScript is much more lightweight for expressing functionality. It's hard to prove this with words, but JSON, dynamic typing, lambda notation, prototypal inheritance, lightweight modules, whatever ... it just tends to take less code to express the same ideas.
  • Con: Maybe you really, really like coding services in Java?

For another perspective on JavaScript and Node.js, check out From Java to Node.js, a blog post on a Java developer's impressions and experiences learning Node.js.

Modules When considering node, keep in mind that your choice of JavaScript libraries will DEFINE your experience. Most people use at least two, an asynchronous pattern helper (Step, Futures, Async), and a JavaScript sugar module (Underscore.js).

Helper / JavaScript Sugar:

  • Underscore.js - use this. Just do it. It makes your code nice and readable with stuff like _.isString(), and _.isArray(). I'm not really sure how you could write safe code otherwise. Also, for enhanced command-line-fu, check out my own Underscore-CLI.

Asynchronous Pattern Modules:

  • Step - a very elegant way to express combinations of serial and parallel actions. My personal reccomendation. See my post on what Step code looks like.
  • Futures - much more flexible (is that really a good thing?) way to express ordering through requirements. Can express things like "start a, b, c in parallel. When A, and B finish, start AB. When A, and C finish, start AC." Such flexibility requires more care to avoid bugs in your workflow (like never calling the callback, or calling it multiple times). See Raynos's post on using futures (this is the post that made me "get" futures).
  • Async - more traditional library with one method for each pattern. I started with this before my religious conversion to step and subsequent realization that all patterns in Async could be expressed in Step with a single more readable paradigm.
  • TameJS - Written by OKCupid, it's a precompiler that adds a new language primative "await" for elegantly writing serial and parallel workflows. The pattern looks amazing, but it does require pre-compilation. I'm still making up my mind on this one.
  • StreamlineJS - competitor to TameJS. I'm leaning toward Tame, but you can make up your own mind.

Or to read all about the asynchronous libraries, see this panel-interview with the authors.

Web Framework:

  • Express Great Ruby on Rails-esk framework for organizing web sites. It uses JADE as a XML/HTML templating engine, which makes building HTML far less painful, almost elegant even.
  • jQuery While not technically a node module, jQuery is quickly becoming a de-facto standard for client-side user interface. jQuery provides CSS-like selectors to 'query' for sets of DOM elements that can then be operated on (set handlers, properties, styles, etc). Along the same vein, Twitter's Bootstrap CSS framework, Backbone.js for an MVC pattern, and Browserify.js to stitch all your JavaScript files into a single file. These modules are all becoming de-facto standards so you should at least check them out if you haven't heard of them.


  • JSHint - Must use; I didn't use this at first which now seems incomprehensible. JSLint adds back a bunch of the basic verifications you get with a compiled language like Java. Mismatched parenthesis, undeclared variables, typeos of many shapes and sizes. You can also turn on various forms of what I call "anal mode" where you verify style of whitespace and whatnot, which is OK if that's your cup of tea -- but the real value comes from getting instant feedback on the exact line number where you forgot a closing ")" ... without having to run your code and hit the offending line. "JSHint" is a more-configurable variant of Douglas Crockford's JSLint.
  • Mocha competitor to Vows which I'm starting to prefer. Both frameworks handle the basics well enough, but complex patterns tend to be easier to express in Mocha.
  • Vows Vows is really quite elegant. And it prints out a lovely report (--spec) showing you which test cases passed / failed. Spend 30 minutes learning it, and you can create basic tests for your modules with minimal effort.
  • Zombie - Headless testing for HTML and JavaScript using JSDom as a virtual "browser". Very powerful stuff. Combine it with Replay to get lightning fast deterministic tests of in-browser code.
  • A comment on how to "think about" testing:
    • Testing is non-optional. With a dynamic language like JavaScript, there are very few static checks. For example, passing two parameters to a method that expects 4 won't break until the code is executed. Pretty low bar for creating bugs in JavaScript. Basic tests are essential to making up the verification gap with compiled languages.
    • Forget validation, just make your code execute. For every method, my first validation case is "nothing breaks", and that's the case that fires most often. Proving that your code runs without throwing catches 80% of the bugs and will do so much to improve your code confidence that you'll find yourself going back and adding the nuanced validation cases you skipped.
    • Start small and break the inertial barrier. We are all lazy, and pressed for time, and it's easy to see testing as "extra work". So start small. Write test case 0 - load your module and report success. If you force yourself to do just this much, then the inertial barrier to testing is broken. That's <30 min to do it your first time, including reading the documentation. Now write test case 1 - call one of your methods and verify "nothing breaks", that is, that you don't get an error back. Test case 1 should take you less than one minute. With the inertia gone, it becomes easy to incrementally expand your test coverage.
    • Now evolve your tests with your code. Don't get intimidated by what the "correct" end-to-end test would look like with mock servers and all that. Code starts simple and evolves to handle new cases; tests should too. As you add new cases and new complexity to your code, add test cases to exercise the new code. As you find bugs, add verifications and / or new cases to cover the flawed code. When you are debugging and lose confidence in a piece of code, go back and add tests to prove that it is doing what you think it is. Capture strings of example data (from other services you call, websites you scrape, whatever) and feed them to your parsing code. A few cases here, improved validation there, and you will end up with highly reliable code.

Also, check out the official list of recommended Node.js modules. However, GitHub's Node Modules Wiki is much more complete and a good resource.

To understand Node, it's helpful to consider a few of the key design choices:

Node.js is EVENT BASED and ASYNCHRONOUS / NON-BLOCKING. Events, like an incoming HTTP connection will fire off a JavaScript function that does a little bit of work and kicks off other asynchronous tasks like connecting to a database or pulling content from another server. Once these tasks have been kicked off, the event function finishes and Node.js goes back to sleep. As soon as something else happens, like the database connection being established or the external server responding with content, the callback functions fire, and more JavaScript code executes, potentially kicking off even more asynchronous tasks (like a database query). In this way, Node.js will happily interleave activities for multiple parallel workflows, running whatever activities are unblocked at any point in time. This is why Node.js does such a great job managing thousands of simultaneous connections.

Why not just use one process/thread per connection like everyone else? In Node.js, a new connection is just a very small heap allocation. Spinning up a new process takes significantly more memory, a megabyte on some platforms. But the real cost is the overhead associated with context-switching. When you have 10^6 kernel threads, the kernel has to do a lot of work figuring out who should execute next. A bunch of work has gone into building an O(1) scheduler for Linux, but in the end, it's just way way more efficient to have a single event-driven process than 10^6 processes competing for CPU time. Also, under overload conditions, the multi-process model behaves very poorly, starving critical administration and management services, especially SSHD (meaning you can't even log into the box to figure out how screwed it really is).

Node.js is SINGLE THREADED and LOCK FREE. Node.js, as a very deliberate design choice only has a single thread per process. Because of this, it's fundamentally impossible for multiple threads to access data simultaneously. Thus, no locks are needed. Threads are hard. Really really hard. If you don't believe that, you haven't done enough threaded programming. Getting locking right is hard and results in bugs that are really hard to track down. Eliminating locks and multi-threading makes one of the nastiest classes of bugs just go away. This might be the single biggest advantage of node.

But how do I take advantage of my 16 core box?

Two ways:

  1. For big heavy compute tasks like image encoding, Node.js can fire up child processes or send messages to additional worker processes. In this design, you'd have one thread managing the flow of events and N processes doing heavy compute tasks and chewing up the other 15 CPUs.
  2. For scaling throughput on a webservice, you should run multiple Node.js servers on one box, one per core, using cluster (With Node.js v0.6.x, the official "cluster" module linked here replaces the learnboost version which has a different API). These local Node.js servers can then compete on a socket to accept new connections, balancing load across them. Once a connection is accepted, it becomes tightly bound to a single one of these shared processes. In theory, this sounds bad, but in practice it works quite well and allows you to avoid the headache of writing thread-safe code. Also, this means that Node.js gets excellent CPU cache affinity, more effectively using memory bandwidth.

Node.js lets you do some really powerful things without breaking a sweat. Suppose you have a Node.js program that does a variety of tasks, listens on a TCP port for commands, encodes some images, whatever. With five lines of code, you can add in an HTTP based web management portal that shows the current status of active tasks. This is EASY to do:

var http = require('http');
http.createServer(function (req, res) {
    res.writeHead(200, {'Content-Type': 'text/plain'});
}).listen(1337, "");

Now you can hit a URL and check the status of your running process. Add a few buttons, and you have a "management portal". If you have a running Perl / Python / Ruby script, just "throwing in a management portal" isn't exactly simple.

But isn't JavaScript slow / bad / evil / spawn-of-the-devil? JavaScript has some weird oddities, but with "the good parts" there's a very powerful language there, and in any case, JavaScript is THE language on the client (browser). JavaScript is here to stay; other languages are targeting it as an IL, and world class talent is competing to produce the most advanced JavaScript engines. Because of JavaScript's role in the browser, an enormous amount of engineering effort is being thrown at making JavaScript blazing fast. V8 is the latest and greatest javascript engine, at least for this month. It blows away the other scripting languages in both efficiency AND stability (looking at you, Ruby). And it's only going to get better with huge teams working on the problem at Microsoft, Google, and Mozilla, competing to build the best JavaScript engine (It's no longer a JavaScript "interpreter" as all the modern engines do tons of JIT compiling under the hood with interpretation only as a fallback for execute-once code). Yeah, we all wish we could fix a few of the odder JavaScript language choices, but it's really not that bad. And the language is so darn flexible that you really aren't coding JavaScript, you are coding Step or jQuery -- more than any other language, in JavaScript, the libraries define the experience. To build web applications, you pretty much have to know JavaScript anyway, so coding with it on the server has a sort of skill-set synergy. It has made me not dread writing client code.

Besides, if you REALLY hate JavaScript, you can use syntactic sugar like CoffeeScript. Or anything else that creates JavaScript code, like Google Web Toolkit (GWT).

Speaking of JavaScript, what's a "closure"? - Pretty much a fancy way of saying that you retain lexically scoped variables across call chains. ;) Like this:

var myData = "foo";
database.connect( 'user:pass', function myCallback( result ) {
    database.query("SELECT * from Foo where id = " + myData);
} );
// Note that doSomethingElse() executes _BEFORE_ "database.query" which is inside a callback

See how you can just use "myData" without doing anything awkward like stashing it into an object? And unlike in Java, the "myData" variable doesn't have to be read-only. This powerful language feature makes asynchronous-programming much less verbose and less painful.

Writing asynchronous code is always going to be more complex than writing a simple single-threaded script, but with Node.js, it's not that much harder and you get a lot of benefits in addition to the efficiency and scalability to thousands of concurrent connections...

by anonymous   2017-08-20

Douglas Crockford's - Code Conventions for the JavaScript Programming Language would be a good place to start.

I learned a lot of useful information in regards to code convention through his video tutorials, which I suggest viewing. I posted the link to the first video out of the four in the series.

Also, as suggested by Ben, (which is a book I would also highly recommend) is Douglas Crockford's book JavaScript: The Good Parts

If you want to find good explanations on jQuery, check out the creator, lead developer and fellow StackOverflower John Resig's website/personal blog.

by anonymous   2017-08-20

Should I using other patterns?

No, you should not insist on a single pattern.

No design pattern books will ever advise you to use a single pattern. Just like you cannot chop all ingredients in one single way (are you going to dice the spaghetti?), you cannot organise all logic in one single pattern.

Sure, you can make all your Objects use the initialiser pattern, and don't use constructors at all. This is ok. Been there, done that. I like it.

But these objects can be used with Builder or Abstract Factory (if it make things simpler). As long as the builders/factories themselves have initialiser, and that they properly initialise the created objects, then your use of the initialiser pattern will be consistent. Outside of creational patterns, it is usually good to organise objects with structural and behavioural patterns. They do not conflict with initialiser at all.

For example, look at DOM. All nodes are created by the Document object - elements, text nodes, comments, even events. This is the Factory pattern.

Yet the Document object is also a Facade! From it you access the whole system's status, objects, data, you can even write to it! Every DOM operation starts from the Document, it is the Facade of the DOM system.

DOM nodes also implements multiple patterns. They are organised in Composite, let you listen to events with Observer and Command, and handle events in a Chain of Responsibility. They are certainly parsed by an Interpreter, DocumentFragment is a Proxy, svg elements are implemented as Decorators, and createNodeIterator obviously gives you an Iterator.

The point is, good object-oriented design will yield multiple design patterns as a result, intentional or not.

What are the secrets for good code appearance

I think the best looking code is the one that is easiest to understand to you, and the way you read code changes as you gain more experience.

For example my style is too condensed for most programmers, but to me it strikes a good balance. So do develop your own style - you are not me, and you are not yesterday's you either.

Remember this as we go through the styles.

At the lowest level we have coding style - most importantly indent and bracket.

This one is simple, pick the one you like and stick with it. There are language specific styles, and they are often good starting points. Configure your IDE's formatter so that you can format all your code with hotkey.

Above the code syntax we have comment style and naming convention.

Setting rules on comment is fine, sometimes it is necessary for documenting tools. Avoid too much comment in practice. You may also want to decide your namespace and your stand on naming function expressions.

Above these structures, we have logic conventions.

The same code logic can often be done in many ways, some more 'beautiful' than the others in your eyes. Look at this example.

I picked the second style on first sight: no duplicate, logic is sectioned cleanly, format is not my style but reasonable. But many programmers would prefer the first style: logic is plain as day, a few duplications is worth it. While abstract, this level is quite deep - present your logic the wrong way actually increase the chance an experienced programmer read it wrong.

Finally, we arrives at the level of design pattern, about as far as code beauty goes.

The key to keep your code structure beautiful, is using the right patterns at right level to consistently accomplish loose coupling and code reuse, while avoiding pitfalls and over-design.

There are quite some books about beautiful code, and then there are even more books about designing and implementing beautiful software. (Decide for yourself which are beyond your level.) Knowledge is as important as experience, and you can gain them only by spending your time to study, to write, and to revise/refactor your apps.

Feel free to change your mind as you explore and experiment with your code. Changing your mind is a good sign of learning.

But first, familiarise yourself with design patterns. Just don't forget, they are the generic result of applying object-oriented principals to common tasks. It is still up to you to do the design.

Design Patterns Are Not Silver Bullets.

by anonymous   2017-08-20

Semicolon insertion strikes again!

    init : function a(s)

needs to be

return {
    init : function a(s)

This is a result of a "feature" in JavaScript that looks at your line with just return on it, and says: "oh, you forgot your semicolon, I'll add it for you."

It changes return to return; so your function now returns undefined, and then you have some naked JSON sitting below it, which is the source of your error. Douglas Crockford actually describes this as one of the "awful parts" of JavaScript.

So the moral of the story is: always put your opening brace on the same line when you're coding in JavaScript.

by anonymous   2017-08-20

Quoting Douglas Crockford from the Good Parts book (page 47), to answer the title of this question:

If the new operator were a method instead of an operator, it could be implemented like this:

Function.method('new', function () {

   // Create a new object that inherits from the 
   // constructor's prototype.

   var that = Object.create(this.prototype);

   // Invoke the constructor, binding -this- to
   // the new object.

   var other = this.apply(that, arguments);

   // If its return value isn't an object,
   // substitute the new object.

   return (typeof other === 'object' && other) || that;

The Function.method method is implemented as follows. This adds an instance method to a class (Source):

Function.prototype.method = function (name, func) {
   this.prototype[name] = func;
   return this;

Further reading:

  • Mozilla Dev Center: Object.create()
  • Mozilla Dev Center: Function.apply()
  • Douglas Crockford: Classical Inheritance in JavaScript