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JSHint - Customising your hurt feelings

As I've started making greater use of JavaScript to give a richer GUI experience the amount of JS in my ASP.NET apps has unsurprisingly ballooned. If I'm honest, I hadn't given much consideration to the code quality of my JavaScript in the past. However, if I was going to make increasing use of it (and given the way the web is going at the moment I'd say that's a given) I didn't think this was tenable position to maintain. A friend of mine works for Coverity which is a company that provides tools for analysing code quality. I understand, from conversations with him, that their tools provide static analysis for compiled languages such as C++ / C# / Java etc. I was looking for something similar for JavaScript. Like many, I have read and loved Douglas Crockford's "JavaScript: The Good Parts"; it is by some margin the most useful and interesting software related book I have read.So I was aware that Crockford had come up with his own JavaScript code quality tool called JSLint. JSLint is quite striking when you first encounter it:

It's the "Warning! JSLint will hurt your feelings." that grabs you. And it's not wrong. I've copied and pasted code that I've written into JSLint and then gasped at the reams of errors JSLint would produce. I subsequently tried JSLint-ing various well known JS libraries (jQuery etc) and saw that JSLint considered they were thoroughly problematic as well. This made me feel slightly better. It was when I started examining some of the "errors" JSLint reported that I took exception. Yes, I took exception to exceptions! (I'm *very* pleased with that!) Here's a few of the errors generated by JSLint when inspecting jquery-1.7.2.js: - Problem at line 16 character 10: Expected exactly one space between 'function' and '('.

  • Problem at line 25 character 1: Expected 'var' at column 13, not column 1.
  • Problem at line 31 character 5: Unexpected dangling '_' in '_jQuery'.

JSLint is, much like it's creator, quite opinionated. Which is no bad thing. Many of Crockfords opinions are clearly worth their salt. It's just I didn't want all of them enforced upon me. As you can see above most of these "problems" are essentially complaints about a different style rather than bugs or potential issues. Now there are options in JSLint that you can turn on and off which looked quite promising. But before I got to investigating them I heard about JSHint, brainchild of Anton Kovalyov and Paul Irish. In their own words: JSHint is a fork of JSLint, the tool written and maintained by Douglas Crockford. The project originally started as an effort to make a more configurable version of JSLint—one that doesn't enforce one particular coding style on its users—but then transformed into a separate static analysis tool with its own goals and ideals. This sounded right up my alley! So I thought I'd repeat my jQuery test. Here's a sample of what JSHint threw back at me, with its default settings in place: - Line 230: return num == null ? Expected '===' and instead saw '=='.

  • Line 352: if ( (options = arguments[ i ]) != null ) { Expected '!==' and instead saw '!='.
  • Line 354: for ( name in options ) { The body of a for in should be wrapped in an if statement to filter unwanted properties from the prototype.

These were much more the sort of "issues" I was interested in. Plus it seemed there was plenty of scope to tweak my options. Excellent. This was good. The icing on my cake would have been a plug-in for Visual Studio which would allow me to evaluate my JS files from within my IDE. Happily the world seems to be full of developers doing good turns for one another. I discovered an extension for VS called JSLint for Visual Studio 2010:

This was an extension that provided either JSLint *or* JSHint evaluation as you preferred from within Visual Studio. Fantastic! With this extension in play you could add JavaScript static code analysis to your compilation process and so learn of all the issues in your code at the same time, whether they lay in C# or JS or [insert language here]. You could control how JS problems were reported; as warnings, errors etc. You could straightforwardly exclude files from evaluation (essential if you're reliant on a number of 3rd party JS libraries which you are not responsible for maintaining). You could cater for predefined variables; allow for jQuery or DOJO. You could simply evaluate a single file in your solution by right clicking it and hitting the "JS Lint" option in the context menu. And it was simplicity itself to activate and deactivate the JSHint / JSLint extension as required. For a more exhaustive round up of the options available I advise taking a look here: I would heartily recommend using JSHint if you're looking to improve your JS code quality. I'm grateful to Crockford for making JSHint possible by first writing JSLint. For my part though I think JSHint is the more pragmatic and useful tool and likely to be the one I stick with. For interest (and frankly sheer entertainment value at the crotchetiness of Crockford) it's definitely worth having a read up on how JSHint came to pass: -

The Joy of JSON

So back to JSON. For those of you that don't know JSON stands for JavaScript Object Notation and is lightweight text based data interchange format. Rather than quote other people verbatim you can find thorough explanations of JSON here: - Introducing JSON

As mentioned in my previous post on Ajax I came upon JSON quite by accident and was actually using it for some time without having any idea. But let's pull back a bit. Let's start with the JavaScript Object Literal. Some years ago I came upon this article by Christan Heilmann about the JavaScript Object Literal which had been published all the way back in 2006: Show love to the JavaScript Object Literal Now when I read this it was a revelation to me. I hadn't really used JavaScript objects a great deal at this point (yes I am one of those people that started using JavaScript without actually learning the thing) and when I had used them is was through the var obj = new Object() pattern (as that's the only approach I knew). So it was wonderful to discover that instead of the needlessly verbose: ```js var myCar = new Object(); myCar.wheels = 4; myCar.colour = "blue";

I could simply use the much more concise object literal syntax to declare an object instead: ```js
var myCar = { wheels: 4, colour: "blue" };

Lovely. Henceforth I adopted this approach in my code as I'm generally a believer that brevity is best. It was sometime later that I happened upon JSON (when I started looking into jqGrid). Basically I was looking to pass complex data structures backward and forward to the server and, as far as I knew, there was no way to achieve this simply in JavaScript. I was expecting that I would have to manually serialise and deserialise (yes dammit I will use the English spellings!) objects when ever I wanted to do this sort of thing. However, I was reading the the fantastic Dave Ward's Encosia blog which on this occasion was talking about the troubles of UpdatePanels (a subject close to my heart by the way) and more interestingly the use of PageMethods in ASP.NET. This is what he said that made me prick up my ears: "Page methods allow ASP.NET AJAX pages to directly execute a page’s static methods, using JSON (JavaScript Object Notation). JSON is basically a minimalistic version of SOAP, which is perfectly suited for light weight communication between client and server." JSON is a lightweight SOAP eh? I've used SOAP. I wonder if I could use this.... To my complete surprise, and may I say delight, I discovered that a wonderful fellow called Douglas Crockford, he of JavaScript, The Good Parts fame had quietly come up with JSON some time ago. JSON, from my perspective, turned out to be a simple way to turn an object into a string and then from a string back into an object. So simple that it consists of 2 methods on a JSON object: - JSON.stringify(myObject) - take an object and make me a JSON string. (and by the way isn't "stringify" just the loveliest method name ever?)

  • JSON.parse(myJSONString) - take a JSON string and make me an object

Let me illustrate the above method names using the myCar example from earlier: ```js var myCar = { wheels: 4, colour: "blue" }; // myCar is an object

var myCarJSON = JSON.stringify(myCar); //myCarJSON will look like this: '{"wheels":4,"colour":"blue"}'

var anotherCarMadeFromMyJSON = JSON.parse(myCarJSON); //anotherCarMadeFromMyJSON will be a brand new "car" object

I've also demonstrated this using the Chrome Console: ![](../static/blog/2012-02-23-joy-of-json/Using%2BJSON.png)
Crockford initially invented/discovered JSON himself and wrote a little helper library which provided a JSON object to be used by all and sundry. This can be found here: [JSON on GitHub](<>) Because JSON was so clearly wonderful, glorious and useful it ended up becoming a part of the EcmaScript 5 spec (in fact it's worth reading the brilliant [John Resig's blog post](<>) on this). This has lead to JSON being offered [natively in browsers](<>) for quite some time. However, for those of us (and I am one alas) still supporting IE 6 and the like we still have Crockfords JSON2.js to fall back on.

JavaScript - getting to know the beast...

So it's 2010 and I've started using jQuery. jQuery is a JavaScript library. This means that I'm writing JavaScript... Gulp! I should say that at this point in time I *hated* JavaScript (I have mentioned this previously). But what I know now is that I barely understood the language at all. All the JavaScript I knew was the result of copying and pasting after I'd hit "view source". I don't feel too bad about this - not because my ignorance was laudable but because I certainly wasn't alone in this. It seems that up until recently hardly anyone knew anything about JavaScript. It puzzles me now that I thought this was okay. I suppose like many people I didn't think JavaScript was capable of much and hence felt time spent researching it would be wasted. Just to illustrate where I was then, here is 2009 John's idea of some pretty "advanced" JavaScript: ```html function GiveMeASum(iNum1, iNum2) { var dteDate = new Date(); var iTotal = iNum1 + iNum2; return "This is your total: " + iTotal + ", at this time: " + dteDate.toString(); }


I know - I'm not to proud of it... Certainly if it was a horse you'd shoot it. Basically, at that point I knew the following: - JavaScript had functions (but I knew only one way to use them - see above)

  • It had some concept of numbers (but I had no idea of the type of numbers I was dealing with; integer / float / decimal / who knows?)
  • It had some concept of strings
  • It had a date object

This was about the limit of my knowledge. If I was right, and that's all there was to JavaScript then my evaluation of it as utter rubbish would have been accurate. I was wrong. SOOOOOOOOOOOO WRONG! I first realised how wrong I was when I opened up the jQuery source to have a read. Put simply I had *no* idea what I was looking at. For a while I wondered if I was actually looking at JavaScript; the code was so different to what I was expecting that for a goodly period I considered jQuery to be some kind of strange black magic; written in a language I did not understand. I was half right. jQuery wasn't black magic. But it was written in a language I didn't understand; namely JavaScript. :-( Here beginneth the lessons... I started casting around looking for information about JavaScript. Before very long I discovered one Elijah Manor who had helpfully done a number of talks and blog posts directed at C# developers (which I was) about JavaScript. My man! - How good C# habits can encourage bad JavaScript habits part 1

For me this was all massively helpful. In my development life so far I had only ever dealt with strongly typed, compiled "classical" languages. I had little to no experience of functional, dynamic and loosely typed languages (essentially what JavaScript is). Elijahs work opened up my eyes to some of the massive differences that exist. He also pointed me in the direction of the (never boring) Doug Crockford, author of the best programming book I have ever purchased: JavaScript: The Good Parts. Who could not like a book about JavaScript which starts each chapter with a quote from Shakespeare and still comes in at only a 100 pages? It's also worth watching the man in person as he's a thoroughly engaging presence. There's loads of videos of him out there but this one is pretty good: Douglas Crockford: The JavaScript Programming Language. I don't want to waste your time by attempting to rehash what these guys have done already. I think it's always best to go to the source so I'd advise you to check them out for yourselves. That said it's probably worth summarising some of the main points I took away from them (you can find better explanations of all of these through looking at their posts): 1. JavaScript has objects but has no classes. Instead it has (what I still consider to be) the weirdest type of inheritance going: prototypical inheritance. 2. JavaScript has the simplest and loveliest way of creating a new object out there; the "JavaScript Object Literal". Using this we can simply var myCar = { wheels: 4, colour: "blue" } and ladies and gents we have ourselves a car! (object) 3. In JavaScript functions are first class objects. This means functions can be assigned to variables (as easily as you'd assign a string to a variable) and crucially you can pass them as parameters to a function and pass them back as a return type. Herein lies power! 4. JavaScript has 6 possible values (false, null, undefined, empty strings, 0 and NaN) which it evaluates as false. These are known as the "false-y" values. It's a bit weird but on the plus side this can lead to some nicely terse code. 5. To perform comparisons in JavaScript you should avoid == and != and instead use === and !==. Before I discovered this I had been using == and != and then regularly puzzling over some truly odd behaviour. Small though it may sound, this may be the most important discovery of the lot as it was this that lead to me actually *trusting* the language. Prior to this I vaguely thought I was picking up on some kind of bug in the JavaScript language which I plain didn't understand. (After all, in any sane universe should this really evaluate to true?: 0 == "") 6. Finally JavaScript has function scope rather than block scope. Interestingly it "hoists" variable declaration to the top of each function which can lead to some very surprising behaviour if you don't realise what is happening.

I now realise that JavaScript is a fantastic language because of it's flexibility. It is also a deeply flawed language; in part due to it's unreasonably forgiving nature (you haven't finished your line with a semi-colon; that's okay - I can see you meant to so I'll stick one in / you haven't declared your variable; not a problem I won't tell you but I'll create a new variable stick it in global scope and off we go etc). It is without question the easiest language with which to create a proper dogs breakfast. To get the best out of JavaScript we need to understand the quirks of the language and we need good patterns. If you're interested in getting to grips with it I really advise you to check out the Elijah and Dougs work - it really helped me.