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

1-js/02-first-steps/14-switch/2-rewrite-if-switch/task.md

@@ -0,0 +1,23 @@
+importance: 4
+
+---
+
+# Rewrite "if" into "switch"
+
+Rewrite the code below using a single `switch` statement:
+
+```js run
+let a = +prompt('a?', '');
+
+if (a == 0) {
+  alert( 0 );
+}
+if (a == 1) {
+  alert( 1 );
+}
+
+if (a == 2 || a == 3) {
+  alert( '2,3' );
+}
+```
+