Sunday, November 27, 2011

About Felix's Style Guide

Style guides are good as long as these are meaningful and a bit "open minded" because if one style is recognized as anti pattern then it must be possible to update/change it.

The Felix's Node.js Style Guide is surely a meaningful one, but I hope it's open minded too.

Why This Post

Because I write node.js code as well sometimes and I would like to write code accepted by the community. Since developers may go too religious about guides I don't want explain all these points per each present or future node.js module I gonna write ... I post it once, I will eventually update it, but it's here and I can simply point at this any time.

Style Guide Side Effect

As happened before with the older one or the linter, a style guide may mislead developers and if they are too religious and unable to think about some point, the quality of the result code may be worse rather than better.
I have talked about JSLint already too much in this blog so ... let's bring the topic in track and see what Felix may re-consider.


Current status: Use single quotes, unless you are writing JSON
A common mistake for JavaScript developers, specially those with PHP, Ruby, or other scripting languages background, is to think that single quotes are different from double quotes ... sorry to destroy this myth guys but in JavaScript there is no difference between single and double quotes.
Once you get this, you must think that if by standard definition JSON uses double quotes there is no reason to prefer single quotes over double.
What should this difference tell us, that one is JSON and one is JavaScript for node.js? Such assumption is a bit ridiculous to me since JSON is JavaScript, nothing more, nothing less.
More over, I am not a big fan of HTML strings inside JS files because of separation of concerns, and I'll come back on it, but in English, as well as in many other languages, the single quote inside a string is quite common, isn't it?
Accordingly, are you really planning to prefer 'it\'s OK' over "it's OK"?
And if the suggested editor, in the guide itself, is one with supported syntax highlight, shouldn't we simply trust the highlighted string in order to recognize it, rather than distinguish between JSON and non JSON strings?
Shouldn't we write comfortably without silly rules, as Felix says in another point, so that we can chose whatever string delimiter we want accordingly with the content of the string?
Last, but not least, for those convinced that in HTML there is any sort of difference between single and double quotes, I am sorry to, once again, destroy this myth since there is no difference in HTML between quotes ... so, once again, chose what you want and focus on something else than distinction between JSON and non JSON strings ...

Variable declarations

Current status: Declare one variable per var statement, it makes it easier to re-order the lines. Ignore Crockford on this, and put those declarations wherever they make sense.
If there is one thing that I always agreed with Crockford is this one: variable declared at the beginning of the function, with the exception for function declarations that should be before variable declarations, and not after.
The reason is quite simple: wherever we declare a variable, this will be available at the very beginning of the scope so which place can be better than the beginning of the scope itself to instantly recognize all local scope variables rather than scrolling the whole closure 'till the end in order to find that name that completely screwed up the whole logic in the middle because is shadowing something else inside or outside the scope ?
Is that easy, I don't want to read potentially thousands of lines of code to understand which variable has been defined where, I want a single bloody place to understand what is local and what is not.
The only exception to this rule may be some temporary variable, as is the classic i used in for loops, or some tmp reference still common in for loops

// the exception ... in the middle of the code

for (var i = 0, length = something.length, tmp; i < length; ++i) {
tmp = something[i];
// do something meaningful

Chances that above loop will destroy our logic because of a shadowed i or tmp reference are really rare and we should use meaningful variables name.
As summary, there are only advantages on declaring variables on top, and until we have no let statements it is only risky, and dangerous for our business, to define variables in the wild.

// how you may write code
(function () {
return true;
var inTheWild = 123;
function checkTheWild() {
return inTheWild === 123;

// how JS works in any case
(function () {

// function declarations instantly available in the scope
function checkTheWild() {
return inTheWild === 123;

// any var declaration instantly available as undefined
var inTheWild;

return true;

// no matters where/if we assign the value
// the inTheWild is already available everywhere
// with undefined as default value
// and before this assignment
inTheWild = 123;

// shadows should be easy to track
// top of the function is the right place to track them


Current status: Constants should be declared as regular variables or static class properties, using all uppercase letters.

Node.js / V8 actually supports mozilla's const extension, but unfortunately that cannot be applied to class members, nor is it part of any ECMA standard.

I could not disagree more here ... the meaning of constant is something immutable and the reason we use constant is to believe these are immutable.
Why on earth avoid a language feature when it provides exactly what we need? Don't we want more reliable code? And what about security?
Neither in PHP we can define an object property and this does not mean we should avoid the usage of define function, isn't it?
Use const as much as you want unless the code does not have to run cross platform ( browsers included ) and if you want to define constants with objects, use the JavaScript equivalent to do that.

function define(object, property, value) {
Object.defineProperty(object, property, {
get: function () {
return value;
// if you really want to throw an error
// , set: function () {throw "unable to redefine " + property;}

var o = {};
define(o, "TEST", 123);
o.TEST = 456;
o.TEST; // 123

I have personally proposed cross platform ways to do the same without or within objects themselves.
As we can see there are many ways to define constants and if the argument is that const is not standard it's a weak one because nobody is planning to remove this keyword from V8 or SpiderMonkey, most likely every other browser will adopt this keyword in the future but if that won't happen, to find and replace it with var only when necessary is a better way to go: security and features, we should encourage these things rather than ignore them, imho.

Equality operator

Current status: Programming is not about remembering stupid rules. Use the triple equality operator as it will work just as expected.
No it doesn't because coercion is not about equality only.

alert("2" < 3 && 1 < "2");

Programming IS about remembering rules, that's the reason we need to know the syntax in order to code something ... right?
Coercion must be understood rather than being ignored and rules are pretty much simple and widely explained in the specs, even more simplified in this old post of mine.
If any of you developers still do this idiotic check you are doing it wrong.

// WRONG!!!!!!!!!!!!!
arg === null || arg === undefined

arg == null

You should rather avoid undefined equality in any piece of code you wrote, unless you did not create an undefined reference by yourself.
As summary, a good developer does not ignore problems, a good developer understands them and only after decide which way is the best one.
Felix is a good developer and he should promote deeper knowledge ... this specific point was really bad because it's like saying "avoid regular expressions because you don't understand them and you don't want to learn them".

Extending prototypes

Current status: Do not extend the prototypes of any objects, especially native ones
Read this article and stick an "it depends" in your screen. Nobody wants to limit JS potentials and Object.defineProperty/ies is a robust way to do things properly.
Sure we must understand that even a method like Array#empty could have different meanings ... e.g.

var arr = Array(3);
// is arr empty ?
// length is 3 but no index has been addressed

If we pollute native prototype we must agree on the meaning or we must prefix our extension so that nobody can complain if that empty was good enough or just a wrong concept.

// a meaningful Array#empty
Object.defineProperty(Array.prototype, "empty", {
value: function empty() {
for (var i in this) return false;
return true;

[].empty(), // true
Array(3).empty(), // true
[null].empty() // false


Current status: Any non-trivial conditions should be assigned to a descriptive variable
I often write empty condition on purpose and to both avoid superflous re-assignment and speed up the code.

// WRONG = || defaultValue;

// better || ( = defaultValue):

"property" in object || ( = defaultValue);

Why on earth would I assign that ? Same I would not do it if the condition is not reused at least twice.

if (done.something() && done.succeed) {
// done.something() && done.succeed useful
// here and nowhere else in the code

Accordingly with the fact spread variable declarations are a bad practice, I cannot think about creating flags all over the place for these kind of one shot checks.

Function length

Current status: Keep your functions short. A good function fits on a slide that the people in the last row of a big room can comfortably read. So don't count on them having perfect vision and limit yourself to ~10 lines of code per function.
I agree on this point but JavaScript is all about functions.
I understand the require approach does not need a closure to surround the whole module, being this already somehow sandboxed, but cross platform code and private functions or variables are really common in JS so that a module may be entirely written inside a closure.
A closure is a function so as long as this point is flexible is fine to me, also as long as the code is still readable and elegant ... I can already imagine developers writing 10 lines of functions using all 80 characters per line in order to respect this point ...

... now, that would be lame.

Object.freeze, Object.preventExtensions, Object.seal, with, eval

Current status: Crazy shit that you will probably never need. Stay away from it.
Felix here put language features together with "language mistakes".
With "use strict" directive, the one Felix should have put at the very beginning of his guideline, with statement is not even allowed.
eval has nothing to do with Object.freeze and others and these methods are part of the ES5 specification.
It is true you may not need them, to define them as something to stay away from, specially from somebody that said there are no constants for objects, is kinda limitative and a sort of non sense.
Learn these new methods, and use them if you think/want/need.

And that's all folks

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