merging all conflicts

Author: iliakan

1-js/02-first-steps/12-nullish-coalescing-operator/article.md

@@ -77,7 +77,21 @@ alert(firstName || lastName || nickName || "Anonymous"); // Supercoder
 */!*
 ```
 
+<<<<<<< HEAD
 Αυτό ορίζει το `height` σε `100` εάν δεν έχει οριστεί.
+=======
+Historically, the OR `||` operator was there first. It's been there since the beginning of JavaScript, so developers were using it for such purposes for a long time.
+
+On the other hand, the nullish coalescing operator `??` was added to JavaScript only recently, and the reason for that was that people weren't quite happy with `||`.
+
+The important difference between them is that:
+- `||` returns the first *truthy* value.
+- `??` returns the first *defined* value.
+
+In other words, `||` doesn't distinguish between `false`, `0`, an empty string `""` and `null/undefined`. They are all the same -- falsy values. If any of these is the first argument of `||`, then we'll get the second argument as the result.
+
+In practice though, we may want to use default value only when the variable is `null/undefined`. That is, when the value is really unknown/not set.
+>>>>>>> 733ff697c6c1101c130e2996f7eca860b2aa7ab9
 
 Ας συκγρίνουμε το `||`:
 

1-js/11-async/03-promise-chaining/article.md

@@ -72,7 +72,7 @@ promise.then(function(result) {
 });
 ```
 
-What we did here is just several handlers to one promise. They don't pass the result to each other; instead they process it independently.
+What we did here is just adding several handlers to one promise. They don't pass the result to each other; instead they process it independently.
 
 Here's the picture (compare it with the chaining above):