In previous writing I discussed the problem of where to
put general-purpose object-manipulation methods (like forEach,
map and reduce methods of Array, but for objects) and concluded
that placing them to Object.prototype is defenetly not a way to go.
So the problem still remains. Lets try another approach.
Object objectPreviously I ended with saying that something like this might work:
var ages = {John: 10, Mary: 20, Phil: 18, Alice: 32};
var avgAge = Object.prototype.average(ages);
That’s of course assuming that we have a way to define non-enumerable
properties (as in upcoming ECMAScript 5). But when we write
our code like that, we don’t really need a prototype any more, so we
can simplify it and add our methods directly to Object:
var avgAge = Object.average(ages);
That’s way better than the previous, because:
we completely avoid all the problems with Object.prototype –
Object is a safe place to add our functions.
we don’t have to wait for next version of JavaScript, and most imprtantly
the code is a lot shorter.
Happy with that, let’s try our new approach out:
// Calculate average age of persons who are over 18
var over18 = Object.filter(ages, function(age) {
return age > 18;
});
var avgAge = Object.reduce(over18, function(a, b) {
return a + b;
}, 0) / Object.count(over18);
This doesn’t look bad, but it doesn’t look particularly good either.
One problem is that now our code is littered with Object.this and
Object.that – typing Object at the beginning of each of our
object-methods seems redundant and too verbose. Especially when you
compare it to array-methods, that don’t require you to ever mention
Array.
When writing Object is tedious we could use something shorter
instead – for our purposes it’s just a container for our static
functions and we aren’t bound to use Object for that.
We could give up on using a container object completely and just
prefix each method with o or obj. So we would have objMap,
objFilter, objReduce etc. But I think my dear reader would not
forgive me polluting the global namespace with a myriad of tiny
functions. So we just skip this thought without further ado.
Instead of Object we could use Obj, Ob or event just O...
But using one-letter global variable names is just asking for trouble.
Ob and Obj are succeedingly more safer, but it would be nice to
have something really-really short while keeping away from conflicts.
One way to achieve this is follow the practice of many JS libraries
and prefix our variable with $. This way we could just use $O.
So lets write the previous example again using our new notation:
// Calculate average age of persons who are over 18
var over18 = $O.filter(ages, function(age) {
return age > 18;
});
var avgAge = $O.reduce(over18, function(a, b) {
return a + b;
}, 0) / $O.count(over18);
That’s quite a bit less typing. Lets try something without intermediate variables, something that could possibly be a one-liner:
// find names of the first-born children
var people = {
John: ["Mary", "Thomas", "Mat"],
Alice: [],
Carol: ["Bob", "Tom"]
}
// first filter out people who have children
// then get the first child of each of them
// finally discard parents, keeping only child names
var chNames = $O.values($O.map($O.filter(people, function(children) {
return children.length > 0;
}), function(children) {
return children[0];
}));
Now this thing is pretty intimidating to read. It kind of reads backwards. Not like when reading chained-together array-methods, which tend to follow each other quite naturally. But we would really like to combine the methods together and this kind of degradation in readability is not acceptable.
Compared to using Object.prototype this method is safe to use, but
it has huge drawbacks on readability. When you don’t need to combine
your object-manipulation-methods, then this technique might be for you,
but the rest of us must look further.
Stay tuned for the next article in this series.
Kirjutatud 4. oktoobril 2009.
RSS, RSS kommentaarid, XHTML, CSS, AA
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Instead of Object we could use Obj, Ob or event just O
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