Use iterators and generators

Author: dimadeveatii

README.md

@@ -981,6 +981,90 @@ inventoryTracker('apples', req, 'www.inventory-awesome.io');
 
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+### Use iterators and generators
+
+Use generators and iterables when working with collections of data used like a stream.  
+There are some good reasons:
+- decouples the callee from the generator implementation in a sense that callee decides how many
+items to access
+- lazy execution, items are streamed on demand
+- built-in support for iterating items using the `for-of` syntax
+- iterables allow to implement optimized iterator patterns
+
+For
+
+**Bad:**
+
+```ts
+function fibonacci(n: number): number[] {
+  if (n === 1) return [0];
+  if (n === 2) return [0, 1];
+
+  const items: number[] = [0, 1]; 
+  while (items.length < n) {
+    items.push(items[items.length - 2] + items[items.length - 1]);
+  }
+
+  return items;
+}
+
+function print(n: number) {
+  fibonacci(n).forEach(fib => console.log(fib));
+}
+
+// Print first 10 Fibonacci numbers.
+print(10);
+```
+
+**Good:**
+
+```ts
+// Generates an infinite stream of Fibonacci numbers.
+// The generator doesn't keep the array of all numbers.
+function* fibonacci(): IterableIterator<number> {
+  let [a, b] = [0, 1];
+ 
+  while (true) {
+    yield a;
+    [a, b] = [b, a + b];
+  }
+}
+
+function print(n: number) {
+  let i = 0;
+  for (const fib in fibonacci()) {
+    if (i++ === n) break;  
+    console.log(fib);
+  }  
+}
+
+// Print first 10 Fibonacci numbers.
+print(10);
+```
+
+There are libraries that allow working with iterables in a simillar way as with native arrays, by
+chaining methods like `map`, `slice`, `forEach` etc. See [itiriri](https://www.npmjs.com/package/itiriri) for
+an example of advanced manipulation with iterables (or [itiriri-async](https://www.npmjs.com/package/itiriri-async) for manipulation of async iterables). 
+
+```ts
+import itiriri from 'itiriri';
+
+function* fibonacci(): IterableIterator<number> {
+  let [a, b] = [0, 1];
+ 
+  while (true) {
+    yield a;
+    [a, b] = [b, a + b];
+  }
+}
+
+itiriri(fibonacci())
+  .take(10)
+  .forEach(fib => console.log(fib));
+```
+
+**[⬆ back to top](#table-of-contents)**
+
 ## Objects and Data Structures
 
 ### Use getters and setters