28.03.15. Одесса. Impact Hub Odessa. Конференция JSLab. Домников Виталий. "ES6 генераторы и Koa.js" Доклад про ES6 generators, для чего они нужны и как мы до этого докатились и пример использования в Koa.js Подробнее: http://geekslab.co/ https://www.facebook.com/GeeksLab.co https://www.youtube.com/user/GeeksLabVideo

1. ES6 GENERATORS
AND KOA.JS

2. VITALY DOMNIKOV
GITHUB: @DOTCYPRESS
TWITTER: @DOTCYPRESS

3. HAPPY JS DEVELOPMENT
fs.readFile(inputFile, function (err, data) {
if (err) return res.status(500).send(err);
process1(data, function (err, data) {
if (err) return res.status(500).send(err);
process2(data, function (err, data) {
if (err) return res.status(500).send(err);
process3(data, function (err, data) {
if (err) return res.status(500).send(err);
fs.writeFile(outputFile, data, function (err) {
if (err) return res.status(500).send(err);
res.status(200).send('YEAH');
});
});
});
});
});

5. MIRACLE
//node --harmony sample.js
var sampleGenerator = function *() {
yield 1;
yield 2;
}
var generator = sampleGenerator();
console.log(generator.next()); // { value: 1, done: false }
console.log(generator.next()); // { value: 2, done: false }
console.log(generator.next()); // { value: undefined, done: true }

6. GENERATORS METHODS
next()
This is used to resume the execution.
generator.next();
// Result:
{
value: 1,
done: false
}

7. GENERATORS METHODS
throw()
This is used to throw an error or exception at any
step.
generator.throw(new Error("BSOD"));

9. FIBBONACI
var fibbonaciGenerator = function *() {
var acc = 1;
var result = 0;
while (true) {
yield result;
var temp = result;
result += acc;
acc = temp;
}
};
var generator = fibbonaciGenerator();
console.log(generator.next()); // { value: 0, done: false }
console.log(generator.next()); // { value: 1, done: false }
console.log(generator.next()); // { value: 1, done: false }
console.log(generator.next()); // { value: 2, done: false }

10. DELEGATING YIELD
var sampleGenerator = function *() {
yield 1;
yield 2;
}
var delegatedGenerator = function *() {
yield* sampleGenerator();
yield 3;
yield 4;
}
var generator = delegatedGenerator();
console.log(generator.next()); // { value: 1, done: false }
console.log(generator.next()); // { value: 2, done: false }
console.log(generator.next()); // { value: 3, done: false }
console.log(generator.next()); // { value: 4, done: true }

11. CO
GENERATOR BASED CONTROL FLOW
GOODNESS FOR NODEJS AND THE
BROWSER, USING PROMISES,
LETTING YOU WRITE NON­BLOCKING
CODE IN A NICE­ISH WAY.
https://github.com/tj/co

12. CO
The "yieldable" objects currently supported are:
promises
thunks (functions)
array (parallel execution)
objects (parallel execution)
generators (delegation)
generator functions (delegation)

13. CO SAMPLE
var co = require('co');
var thunkify = require('thunkify');
var request = require('request');
var get = thunkify(request.get);
co(function *(){
var a = yield get('http://google.com');
var b = yield get('http://yahoo.com');
var c = yield get('http://cloudup.com');
console.log(a[0].statusCode);
console.log(b[0].statusCode);
console.log(c[0].statusCode);
})();

14. THUNKIFY
TURN A REGULAR NODE FUNCTION
INTO ONE WHICH RETURNS A
THUNK.
https://github.com/tj/node­thunkify
var thunkify = require('thunkify');
var fs = require('fs');
var read = thunkify(fs.readFile);
read('package.json', 'utf8')(function(err, str){
});

16. KOA.JS
NEXT GENERATION WEB
FRAMEWORK FOR NODE.JS
http://koajs.com/

17. HELLO WORLD
var koa = require('koa');
var app = koa();
app.use(function *(){
this.body = 'Hello World';
});
app.listen(3000);

18. CASCADING
var koa = require('koa');
var app = koa();
app.use(function *(next){
var start = new Date;
yield next;
var ms = new Date - start;
this.set('X-Response-Time', ms + 'ms');
});
app.use(function *(){
this.body = 'Hello World';
});
app.listen(3000);

19. CONTEXT
app.use(function *(){
this; // is the Context
this.request; // is a koa Request.
this.response; // is a koa Response.
this.req; // nodejs request.
this.res; // nodejs response.
});

20. ERROR HANDLING
app.use(function *(next) {
try {
yield next;
} catch (err) {
this.app.emit('error', err, this);
this.throw(500, 'Houston we have a problem')
}
});

21. BATTERIES NOT INCLUDED
Routing
File Serving
Compression
Caching
Authentication
Sessions
etc.
KOA middlewares