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

1-js/02-first-steps/15-function-basics/3-min/solution.md

@@ -0,0 +1,21 @@
+A solution using `if`:
+
+```js
+function min(a, b) {
+  if (a < b) {
+    return a;
+  } else {
+    return b;
+  }
+}
+```
+
+A solution with a question mark operator `'?'`:
+
+```js
+function min(a, b) {
+  return a < b ? a : b;
+}
+```
+
+P.S. In the case of an equality `a == b` it does not matter what to return.