What's difference between "reduce" and "scan" : <p>I'm studying RXJS and stuck with the problem: the same code with operators "reduce" and "scan" works in different ways, but I think that must return equal result.
Example below.
Please help.</p>

<pre><code>const txtElement1 = document.getElementById('txt1');
const txtElement2 = document.getElementById('txt2');
const txtElement3 = document.getElementById('txt3');

// function return Observable
function get(array, initValue) {
  return Rx.Observable.create(observer =&gt; {
    let timer = initValue;

    array.forEach(item =&gt; {
      setTimeout(() =&gt; observer.next(item), timer);
      timer += 1000;
    });
  });
}

// 1) don't work with "reduce"
var stream1$ = get(['John', 'Ann', 'Bob'])
  .reduce(function(acc, x) {
    return acc + ` ${x}`;
  }, 'first - ');

stream1$.subscribe(text =&gt; txtElement1.innerHTML = text);

// 2)  the same code, but with "scan" - working
var stream2$ = get(['John', 'Ann', 'Bob'])
  .scan(function(acc, x) {
    return acc + ` ${x}`;
  }, 'second - ');

stream2$.subscribe(text =&gt; txtElement2.innerHTML = text);

// 3)  and the simple Observable with "reduce" - working
var stream3$ = Rx.Observable.from(['John', 'Ann', 'Bob'])
  .reduce(function(acc, x) {
    return acc + ` ${x}`;
  }, 'third - ');

stream3$.subscribe(text =&gt; txtElement3.innerHTML = text);
</code></pre>
