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

1-js/02-first-steps/13-while-for/1-loop-last-value/task.md

@@ -0,0 +1,15 @@
+importance: 3
+
+---
+
+# Last loop value
+
+What is the last value alerted by this code? Why?
+
+```js
+let i = 3;
+
+while (i) {
+  alert( i-- );
+}
+```