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

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

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+The first two checks turn into two `case`. The third check is split into two cases:
+
+```js run
+let a = +prompt('a?', '');
+
+switch (a) {
+  case 0:
+    alert( 0 );
+    break;
+
+  case 1:
+    alert( 1 );
+    break;
+
+  case 2:
+  case 3:
+    alert( '2,3' );
+*!*
+    break;
+*/!*
+}
+```
+
+Please note: the `break` at the bottom is not required. But we put it to make the code future-proof.
+
+In the future, there is a chance that we'd want to add one more `case`, for example `case 4`. And if we forget to add a break before it, at the end of `case 3`, there will be an error. So that's a kind of self-insurance.

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

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+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' );
+}
+```
+