I am probably over thinking, but I am having trouble digesting the Nodejs documentation. I am new to javascript and come from a Java Background.
My question is not about any specific nodejs function just overall understanding. Below I give an example of what I am trying to understand...
When working with a statically typed language like Java it is very clear what types are needed for method calls. A trivial example, if I want to sort an array of int's I can just look at Arrays.sort and see that it takes an int[] (same for other types as well). I can also see that it returns void.
public static void sort(int[] a)
However javascript is a dynamic language thus there are no types for api calls. Take this example in the crypto module
crypto.pbkdf2(password, salt, iterations, keylen, callback)
Asynchronous PBKDF2 applies pseudorandom function HMAC-SHA1 to derive a
key of given length from the given password, salt and iterations.
The callback gets two arguments (err, derivedKey).
So without going out and finding example code, or looking at the nodejs source how do I know the argument types of the function? I realized that it is possible to derive the types by looking at the name (ie callback is a function type) but is there any other way?
For example the documentation says that the callback gets two arguments err and derivedKey. What is the type of derivedKey, what is the type or err? Am I missing something about the documentation? How do you know if you are passing in the right types?
Note: I am already know what the type of derivedKey and err is so I don't need answers like "derivedKey is ...." My question is about overall understanding of the Nodejs documentation for someone coming from a statically typed language and is not specific to crypto.pdkdf2.
Well you are pretty much over thinking. You'll have to guess most of them if it's not explained explicitly. like you can guess iterations and keylen are numbers rather than strings. NodeJS docs explain parameters explicitly when they think you can't guess, or you have to know something additional about it. like in crypto.createCredentials(details) they explain that details is a dictionary and which keys you need to use.
F.i. in case of err and derivedKey, since there is no explicit info, i would have assumed both are strings. If it turns out they are not, i would console.log them in callback function to see what they are.
Documentation could be a lot more clear if they have written down types of all parameters but don't know if it's worth the effort.
I have some experience with C# and Java, and have been programming JavaScript for about a year, so I might be able to frame this.
One aspect of JavaScript is that you can make objects like this, on the spot:
var options = {
name: "something",
age: 9,
what: function() {
return 8;
}
};
Everyone takes advantage of this, so it's a big key to understanding JavaScript libraries.
You can also take the above options object and then go like this:
options.mood = "ok";
In other words, objects are just bundles of properties, and the structure isn't set. You can use language constructs like the for ... in loop to iterate through them. That is to say, the "type" of things like err is basically an associative array.
Callbacks are basically everywhere, so the question becomes how to deal with them. A common pattern is function (err, maybeSomething). Most of the time, you only care if err is "something." That is, you'll go like this a lot:
if (err) {
...
}
Frankly, I do a lot of console.log(err) to see what I'm getting back during development.
After that it's really up to the documentation. Some of it is better than others. You're not really missing anything. About the only "trick" is that sometimes a doc will explain everything at the top.
You'll find yourself going into the source sometimes to find out what exactly a library is doing, but 97% of the time a few quick guesses and checks will get you moving.