madbernard: a long angled pier (Default)
I was just reading my friend Anneke's blog from before she did Hack Reactor. In this post she says
"I’m wrapping my head around Javascript’s call() and apply() methods. These get used a lot, and it’s important to understand just how they work. More immediately, these get used in the Hack Reactor pre-course work that I’m working my way through ..."
That crystallized an opinion in me: I want my learning materials to have opinions, because opinions are context.

Eloquent Javascript presents as a textbook, ie "neutral", but since Marijn Haverbeke is a guy with strong opinions they sometimes leak through and make the book way more valuable to me. Codecademy, on the other hand, just presents one thing after another. Last year I asked Ben-the-housemate to help troubleshooting a switch statement project there, and he had to look up the syntax, despite coding JavaScript every day. He explained that switch statements are almost never used. That kind of thing is gold! I'm happy to learn about switch statements, but knowing what the actual bread and butter of a language is is far more helpful. Anneke passed me the Functional Programming in JavaScript page, where Jafar Husain says,
"[map, filter, concatAll, reduce, & zip] will probably be the most powerful, flexible, and useful functions you'll ever learn."
That's what I'm talking about! I'd love to know enough to be able to debate about what is best in JavaScript. Wrangling in forums (well moderated forums that don't allow personal attacks), or watching such wrangles, is the best way to see all sides of a thing.
madbernard: a long angled pier (Default)
I've been sick this past week, which didn't stop me vs. 6.1 and 6.2, but when I hit 6.3 I couldn't even figure out what he was asking. It's like he's saying, design a protuberance on the center of your face, then use that protuberance to detect a scent. ...Does he mean find your nose, or does he mean build yourself a new nose? That second one seems a bit unnecessary. Or to be less metaphorical, what am I missing? Iterating over arrays and objects seems like a major portion of what we've been doing so far. The emphasis on interface has got to be meaningful, but the gap between that text analysis and understanding the reason behind the question is fairly daunting.

I'm posting now because I at least figured out something, though I'm fairly sure I'm deep in the weeds heading in a direction that would baffle and amaze all who came after me.

I wondered what methods came baked in to objects, like forEach does on arrays. So I googled, and found this StackExchange bit, http://stackoverflow.com/questions/5842654/javascript-get-objects-methods

which lead me to screw around in JSBin seeing what came included in the Object package,
console.log(Object.getOwnPropertyNames(Object)); and
console.log(Object.getOwnPropertyNames(Object.prototype));

And then there were all sorts of interesting things to look up:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object

Moving forward with Object.keys, I tried this out as a start of an attack on 6.3, adding the console.log stuff in the midst of the program when it initially didn't return what I expected. Thanks to my housemate Ben for that general technique! What I was trying to do here is to get it to pull out a value from a Seq object at any given point:

var Seq = function(object) {
this.object = object;
};
Seq.prototype.valueAtI = function(i) {
var keyArray = [];
keyArray.push(Object.keys(Seq));
console.log(keyArray);
for (var j = 0; j < (i || keyArray.length); j++) {
if (j == i)
return keyArray[i];
else
return "There are fewer things in the sequence than that";
}
};

var foo = new Seq;
foo.bar = "baz";
foo.bear = "bearz";
foo.pear = "pearz";

console.log(foo.valueAtI(1));

The results were [[]] / There are fewer things in the sequence than that . I'd varied the value of i, even down to 0 ("undefined"), but it was the second set of brackets that tipped me off. Less broken code below:

Seq.prototype.valueAtI = function(i) {
var keyArray = Object.keys(this);
console.log(keyArray);
for (var j = 0; j < (i || keyArray.length); j++) {
if (j == i)
return keyArray[i];
else
return "There are fewer things in the sequence than that";
}
};

This actually results in an array of the keys of the object. It doesn't do what I meant it to do, and I think I can see why now that I'm writing, but it's pretty late and I'm taking the tiny win.
madbernard: a long angled pier (Default)
People on Amazon and elsewhere seem to agree that they do not grok the Table example, so I was curious to get to it. I also don't read it on first pass. I didn't read the squirrel/phi example last chapter, though, either... This one doesn't seem deeper in the weeds than that, at first pass.

I don't understand polymorphism. Inheritance seems simple, but that may be because I vaguely remember that CodeAcademy Javascript, which I did a year ago, hit that hard. Polymorphism seems like it might be like cell biology... Like, many proteins have zinc fingers, structures that hold out a metal ion to interface with other proteins structures. When you see one, you have an idea what that protein/program is going to be up to. But that's just a guess.

Right now I don't understand something fundamental about wording in Javascript... Like, "line" seemed important in his example, but searching the page, it just suddenly appears in the TextCell constructor. I think it's drawing from the array/object inputs, but I need to track down how. For my own code I suspect I'll be doing a ton of veryLongWordyThingThatExplainsBetter, for awhile.
madbernard: a long angled pier (Default)
There I was on Eloquent Javascript's problem 5.4, http://eloquentjavascript.net/05_higher_order.html#h_jr7hZiuR7+

The for loop seemed simple, but what I came up with wasn't processing "isNaN" as a function.

var every = function (array, compare) {
for (var i = 0; i < array.length; i++) {
if (array.i !== compare)
return false;
else return true;
}
};

console.log(every([NaN, NaN, NaN], isNaN));
// → should be true, but was showing as false
console.log(every([NaN, NaN, 4], isNaN));
// → false


Putting the "compare" in the if condition in () parentheses (because I had a memory that some form of parentheses would make javascript try to find the value of a thing... Thinking about this, that was probably a memory from getting values of keys, done with [], which in this case I believe would flag "compare" as an array) didn't fix it. Trying for != to allow for type conversion didn't fix it.

I looked at the hints, and they didn't talk about making functions do their thing; they talked about setting up the loop like "forEach". I took an abortive stab at redoing the loop to use forEach... This didn't run, and the linter in JSBin was sad about my use of break. (I'm still not sure what's up with break.)

function every (array) {
array.forEach(function(compare) {
if (array !== compare) {
break;
}
else return true;
});
return false;
}


I tabbed over to the annotated book: https://docs.google.com/document/d/1aa2-HtUglQrAps31s4LdTPVsiFb1BxhyjZolxeezzcI/edit?_escaped_fragment_=#!
Predicate functions were never defined in the book so I’ll quickly explain them here.

A predicate function is a function that returns true or false based on some condition. In this problem, we’re using isNaN(testValue), which returns true if testValue is NaN (remember this means not a number), and false otherwise.

Huh. At first that seemed a bit unfair, a new unexplained type of function. But then, a closer reading would have indicated that the compare thing had to be a function; and I'd even previously went back to the appearance of isNaN in Eloquent Javascript and managed to whizz past the part where it was summoned into action like so, isNan("some thing").

The working answer,
var every = function (array, compare) {
for (var i = 0; i < array.length; i++) {
if (!compare(array[i]))
return false;
}
return true;
};

And "some" is trivial from there.

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