harmony-iterators.js

harmony-iterator.js

//
// by Dmitry Soshnikov <dmitry.soshnikov@gmail.com>
// MIT Style License
// see also: http://wiki.ecmascript.org/doku.php?id=strawman:iterators
//

// ---------------------------------------
// 1. Iteration via for-in loop
// ---------------------------------------

var foo = {
  x: 10,
  y: 20
};

// iterate over keys
for (let k in keys(foo)) {
  console.log(k); // x, y
}

// over values
for (let v in values(foo)) {
  console.log(v); // 10, 20
}

// and over properties (keys and values)
for (let [k, v] in properties(foo)) {
  console.log(k, v); // x,10, y,20
}

// the previous is the standard
// iterator of the SpiderMonkey
for (let [k, v] in Iterator(foo)) {
  console.log(k, v); // x,10, y,20
}

// ---------------------------------------
// 2. Manual iteration via generator
// ---------------------------------------

let bar = {
  x: 10,
  y: 20
};

var barKeysGenerator = keys(bar);

console.log(barKeysGenerator.next()); // x
console.log(barKeysGenerator.next()); // y
console.log(barKeysGenerator.next()); // StopIteration

// ---------------------------------------
// Implementation
// ---------------------------------------

// generic iterator
function generate(o, fn) {
  for (var k in o) {
    yield fn(k, o[k]);
  }
}

// by keys
function keys(o) {
  return generate(o, function (k, v) {
    return k;
  });
}

// by values
function values(o) {
  return generate(o, function (k, v) {
    return v;
  });
}

// by properties
function properties(o) {
  return generate(o, function (k, v) {
    return [k, v];
  });
}