Add nullish coalescing to multiple articles, refactor operators, renumber the chapter

1-js/02-first-steps/08-operators/1-increment-order/task.md

@@ -0,0 +1,14 @@
+importance: 5
+
+---
+
+# The postfix and prefix forms
+
+What are the final values of all variables `a`, `b`, `c` and `d` after the code below?
+
+```js
+let a = 1, b = 1;
+
+let c = ++a; // ?
+let d = b++; // ?
+```