More than you wanted to know about JavaScript object creation

I began this journey because I needed to create a new instance of a JavaScript class with a variable number of arguments. Not knowing the number of arguments, I couldn't just write new MyClass(arg[0],arg[1].. etc.), so I had to figure out how to replicate the behaviour of new in some other way.

You may have heard that JavaScript inheritance is prototypal. If you don't know what that means, thin of it as one object inheriting from another by making a copy of the original object. Everything in JavaScript is an object, including functions. You may think that JavaScript has classes. It doesn't. It really just has functions.

JavaScript is prototypal, but it wanted to appeal to programmers that were used to "classical" inheritance, so it included the 'new' keyword that we all love so much. That means you can do things like:

function MyClass(arg1,arg2) { = arg1; = arg2;
this.baz = 3;
var mine = new MyClass('foo','bar');
// == 'foo'
So what's going on? MyClass is called, but there is this 'this' object that isn't declared anywhere. Where did it come from? new created it for us and put it into the scope of the MyClass function. If a function called with 'new' doesn't have a return statement, it returns 'this' by default. You could try to call MyClass by itself, but you would end up creating 3 global variables because this defaults to window. So how do we redefine this? There are two methods on all functions (remember, functions are objects, just like everything else) that let you control the value of this: call and apply.
var foo = { qux: '123' };,'foo','bar');
// == 'foo' && foo.qux == '123'
// if you don't know the exact number of arguments you can use apply
var args = ['foo','bar'];
// apply takes an array for the arguments
You might now be thinking that{},'foo','bar') is the same as new MyClass('foo','bar'). Well, new does a bit more than that. Remember the prototype? Calling new more or less creates a copy of the class's prototype, which is then used as this when calling the function. e.g.

MyClass.prototype.myFunc = function(a,b) { return a+b; };
var mine = new MyClass(...);
// mine.myFunc == function(a,b) { return a+b; }

One brief digression from our quest: John Resig blogged about a way to create classes that are instantiated correctly even if you forget new. An interesting read, but not quite what we need since we may need to instantiate classes not under our control.

So if you create a new object, copy all the properties of MyClass.prototype, and then call MyClass.apply(...), is that the same as new MyClass(...)? Nope. new does some things behind the scenes that you cannot replicate without calling new. e.g.,

var mine = {};
for(var i in MyClass.prototype) {
mine[i] = MyClass.prototype[i];
// mine instanceof MyClass == false

So, what we have is an instance that is almost, but not quite identical to an instance created with new. If you know that the object will only be duck typed, then this is good enough. However, if it's possible that it might end up in an instanceof or have some other low level type check, this isn't good enough. The final trick that you need is new:

function newInstance(type,args) {
var f = function() {};
f.prototype = type.prototype;
var o = new f;
return type.apply(o,args) || o;

By creating a no-arguments function with the same prototype, we can safely use new to get the prototype copying, and then call the constructor using apply. instanceof type (and other checks, like prototype.constructor) will return true, and the new instance will walk and talk like a duck of MyClass.

I'm a nerd. Or do I mean geek?... Hi, my name is Noah.

Aaaand it's Thanksgiving. I'm up late because I just got my slice and I can't stop tinkering.

I think my master's project is dead meat. Yes, JSF component creation is woefully painful and slow. Yes, a framework helps tremendously. Yes, my framework was good, and let you choose your Ajax implementation, and so on.

The problem with all that is that the JSF Ajax implementations suck. And the learning curve for JSF (much less components) sucks. It's just too quirky. Hopefully JSF 2.0 will make component creation easy, enable RESTful services, and will make it easier for newbies and old hands to just get things done. I'd like to hope all of that, but the only positive things I tend to hear about 2.0 are from Ed Burns, who seems like a very nice guy, but whose rhetoric reeks of corporate "gotta toe the line/I think my company is the best ever, is not a dinosaur who is slowly and inconsistently embracing open source, and is a bit too bureaucratic to be able to save Java." JavaScript is it, ya know.

Which brings us to my next topic. Kevin at work is the new Grails evangelist. I have to admit, Groovy is a cool language. If not for the fact that JavaScript is the NBL, I think Groovy would be the weapon of choice. Optional static types, intuitive C like syntax, closures everywhere, functional programming, etc. It's a readable LISP, IMHO. Since we'll probably be using Ext for my next project, (in wonderful freezing cold Pittsburgh, no less...) I thought that I'd take the opportunity to get familiar with it by working up a sample project. It's going quite well, so I must remember to get a few entries out of it (yes the separate tech blog is pretty much dead).

Groovy is a great complement to JavaScript/Ajax programming primarily because the thought processes are the same. There are some more syntactic niceties in Groovy, and there is sadly no Prototype for Groovy, but switching is completely effortless. And if I need to, I can always turn the static types back on and write some Java code. If you are a JEE developer and haven't looked at Grails yet, you need to.

More bulletins as events warrant. Cheers.


In the swing of things

I'm finally starting to feel settled in Austin. It helps to actually live here. Working downtown is pretty cool, and I like the bus. Despite the smells, it's usually a nice ride. I get a lot of reading done; too much in fact. I need a side project, so I'm trying to revive my master's project. We'll see how that goes.

November 10th (Saturday), we are having a BBQ from 3ish to whenever I turn into an angry drunk and kick everyone out. If you're reading this, you're invited. If you're not reading this, something is wrong, please stop before you destroy the universe. Thanks.

I need to read something intellectually stimulating, but I'd prefer fiction. Any ideas? Oh, and happy Halloween.


Living in Austin

There is so much to do here. In the last month I've learned more about bikes, built my own road bike, taken the dogs to two of the off leash dog parks, taken the bus downtown a few times (~30min in which I can read, write or just enjoy the scenery; in a car any of those will get you killed), and fixed 98% of the problems with the house, of which there were several dozen. Oh, and I've been very, very lazy, played video games a lot, and spent probably a week's worth of time on reddit. You may not believe it, but not having a job gets old after a while.

Last night we saw Quiet, Lovely for the first time in a few years, although we had to duck out early as H's stomach bug decided to grace us with one final encore. As an aside, The Mohawk seems like a nice place to get a drink, but until they finish their outside stage, it's a bit small for a decent show. Also, why the heck would you start a show at 10 PM on a Thursday night?!?!?! People who like music sometimes have jobs, do you really think you'll sell more beer by forcing them to leave before the show is over? Tonight, Meryll plays at Stubbs. Going by last night, we should show up at about 3 AM.

I fly to Boston on Sunday to start work. According to my parents, I've been to Boston, but didn't get to see much as I was only -2 months old. Think about it. I hope I like traveling as much as I think I do.


it's not so bad...

One of my committee members dropped out. Since my defense was supposed to be tomorrow, that means postponing it a few weeks while we find another person and give them time to get up to speed. Disappointing, but not that big a deal. We still move on Friday, I'll just have to make one last trip up to Hueco later this month.

Yes, my life will be marginally more stressful between now and then, but there's nothing to do about it, and it's not too bad.

Update: It's really not so bad at all. Another professor, hearing my plight, took pity on my poor soul and has undertaken the herculean effort of digesting my 68 page project document in less than two days. It looks like he'll actually make it too! My defense is postponed only until Wednesday. That doesn't mean it's a sure thing, but it gives me a good shot.


blog, blag, blech

Grad school doesn't leave a lot of room for a social life. Certainly nothing to write about, unless you care about my frustrations with technology. That should change soon. That ends Tuesday, then we move to Austin, have a whole month off, and then start a job that sends me all over the country. My first day is in Boston. That's pretty cool.

Hopefully this will be a journal of cool stuff I do while traveling and when I'm home in Austin. I'm sure I'll also resume a bit of the philosophical bent this blog had long ago, but probably with less of the bad poetry/stream of consciousness/"look how emo I am" content. Stupid emo kids.

I'll be 25 this year. There's no avoiding it, I'm a grownup now. But, that doesn't mean we have to act like our parents.