tj/co

The ultimate generator based flow-control goodness for nodejs (supports thunks, promises, etc)

codeami

@codeami

Thank you @LeonineKing1199 ! for...of works.
I can see I needed to (and have started to) focus more on fundamentals (map verb, vs forEach vs for..of)

LeonineKing1199

@LeonineKing1199

Oh man, once you get good enough at JavaScript, you should embrace iterables with open arms.

There's an absolute crap ton of power in iteration

codeami

@codeami

@assertquality

    getAllLabels: {get: function () {
       return $$('label,h2[id$=title],.txt888,span[class="dib ng-binding"]');
    }},
    getAllButtonTexts: {get: function () {
        return $$('input[id*="Btn"]').getAttribute("value");
    }},

I want a combine above two getters in a single getter function getAllLabelsANDButtonTexts to return both Labels and Button Texts. How to do so?

Sorry my Query in not related to generators. any pointers will be appreciated

LeonineKing1199

@LeonineKing1199

Oh I see, these are keys in an already existing object!

You might have to forgive me, my OOP JS is incredibly weak.

In fact, I don't do much OOP, period.

But in your case, I'd say that you can just create a method and then call return [this.getAllLabels(), this.getAllButtonTexts]

If that's jQuery though, you should cache your selectors

Mark Moore

@mmoo9154

Is this a good place for a n00b to co? If not, can someone point me to a good place to start? Thx.

LeonineKing1199

@LeonineKing1199

This the place to go if you're a newb

Mark Moore

@mmoo9154

I'm a bit down a rathole trying to connect to mongo with a Nod.js app in MSVC 2017 RC... As I was crusing through the mongodb node.js driver docs at http://mongodb.github.io/node-mongodb-native/2.2/reference/ecmascript6/connecting/ I came across co for the first time.

LeonineKing1199

@LeonineKing1199

Oh nice!

Mark Moore

@mmoo9154

Looks interesting, but I don't see a lot of docs on co. Is there a tutorial or a dev guide somewhere?

LeonineKing1199

@LeonineKing1199

There should be a github page with basic examples... Lemme check real fast

https://github.com/tj/co

Yeah, this has examples on its usage

Basically with co, you yield out a Promise and you profit :P

Mark Moore

@mmoo9154

I saw the examples, but they didn't seem to apply to the code on the Mongo Node.js Driver page.

LeonineKing1199

@LeonineKing1199

var db = yield MongoClient.connect(url);

This line?

MongoClient has a connect method which takes a url and then returns a Promise

Mark Moore

@mmoo9154

What does co(function*(){...}); do with the passed in function/iterator?

LeonineKing1199

@LeonineKing1199

Ah, brilliant.

So...

co takes a generator and iterates it for you

Basically, you give co a generator and everytime you yield a Promise, co will call it.next() with the resolved value

Mark Moore

@mmoo9154

I kinda get promises...

LeonineKing1199

@LeonineKing1199

const co = function(genFn) {
  const it = genFn();

  const promise = it.next();
 promise.then((resolvedValue) => it.next());
};

That's kind of how co works

Understanding how co is implemented is interesting for sure

It requires good knowledge of both Promises and generators

To use co, just know that you should yield a Promise

Mark Moore

@mmoo9154

So, where does the connect promise yield to?

LeonineKing1199

@LeonineKing1199

Generators are hecka cool because they represent an isolated executable context

Generators sort of live outside of the main JS event loop

So co is a function that runs in your land and will iterator your generator. Part of iteration in JS means that you can feed values back into your generators

Mark Moore

@mmoo9154

Maybe the idea is that control resumes just below the var db = yield MongoClient.connect(url); line...

LeonineKing1199

@LeonineKing1199

co takes advantage of this. When you yield a Promise to co, co will take that Promise and say, Hey, when this Promise resolves, feed the value back into the generator

Mark Moore

@mmoo9154

Then I can use db

LeonineKing1199

@LeonineKing1199

Inside a generator, execution stops at any yield

Execution only resumes when the iterator's .next() is called

So when you type yield, you're actually suspending execution inside the generator

Mark Moore

@mmoo9154

Execution stops (yields) at any yield... But, on the next call to the iterator, execution resumes just after the yield. Yes?

LeonineKing1199

@LeonineKing1199

Yup

You can yield almost anywhere too, it's crazy

Mark Moore

@mmoo9154

Now I kinda get what's going on.

LeonineKing1199

@LeonineKing1199

Generators in JS are quite the mindfuck if you've never seen anything like it before

Yeah

Where communities thrive

People

Repo info

Activity