514-filter.js

// 読み込むとき、ES6 ( + browserify) だと便利
import Rx from "rx"; // ES6 modules

var images = ["1.png", "2.png", "3.png"];
function loadImages() {
  return Rx.Observable.create(loadImagesObservable);
}
function loadImagesObservable(observer) {
  var index = 0;
  var loadImage = (name) => {
    var elem = document.createElement("image");
    elem.src = name;
    elem.onload = function() {
      observer.onNext(index);
      if (index >= images.length - 1) {
        observer.onCompleted();
      } else {
        loadImage(images[++index]);
      }
    }
  };
  loadImage(images[index]);
  return function() { console.log("廃棄されました。"); };
}
function main() {
  var subscription = loadImages().filter(index => index % 5 === 0).subscribe((index) => {
    console.log(index + "個目を読み込みました");
  }, err => {
    console.log("Observe Error: " + err);
  }, () => {
    console.log("読み込み完了");
  });
}