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

1-js/02-first-steps/13-while-for/4-for-even/task.md

@@ -0,0 +1,9 @@
+importance: 5
+
+---
+
+# Output even numbers in the loop
+
+Use the `for` loop to output even numbers from `2` to `10`.
+
+[demo]