Generators

01.js

function* naturalNumbers(){
  var n = 1;
  while (true){
    yield n++;
  }
}

var numbers = naturalNumbers();

console.log (numbers.next());
console.log (numbers.next());
console.log (numbers.next());
console.log (numbers.next());

02.js

function* naturalNumbers(){
  var n = 1;
  while (n < 3){
    yield n++;
  }
}

var numbers = naturalNumbers();

console.log (numbers.next());
console.log (numbers.next());
//{ value: 2, done: false}

//yepp, out of numbers
console.log (numbers.next());
//{value: undefined, done: true}

03.js

var thunk = require('thunkify');
var fs = require('fs');
var read = thunk(fs.readFile);
var co = require('co');

//will be run sequentially
var sizes = co(function *(){
  var a = yield read('.gitignore');
  var b = yield read('README.md');
  var c = yield read('package.json');
  return [a.length, b.length, c.length];
});

//traditional callbacks
sizes(function (err, lengths) {
  console.log(lengths);
});

04.js

var thunk = require('thunkify');
var fs = require('fs');
var read = thunk(fs.readFile);
var co = require('co');


// co is just for control flow goodness
var sizes = co(function *(){
  var a = read('.gitignore');
  var b = read('README.md');
  var c = read('package.json');
  // note: now it will run in parallel
  return [
    (yield a).length,
    (yield b).length,
    (yield c).length
  ];
});

// won't work, yield can only be used in generator function
yield sizes;

package.json

{
  "name": "generator_example",
  "version": "0.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "license": "ISC",
  "dependencies": {
    "co": "^3.0.6",
    "co-redis": "^1.1.0",
    "redis": "^0.10.1",
    "thunkify": "^2.1.1"
  }
}