Add "deep-update" example.

Author: rickbeerendonk

Diff for: temp/deep-update.js

@@ -0,0 +1,34 @@
+/*! European Union Public License version 1.2 !*/
+/*! Copyright © 2020 Rick Beerendonk          !*/
+
+// Immutable deep update.
+
+function update(obj, keyArray, value) {
+  if (keyArray.length === 0) {
+    return value;
+  }
+
+  const first = keyArray.shift();
+  return {
+    ...obj,
+    [first]: update(obj[first], keyArray, value)
+  };
+}
+
+const obj1 = {
+  data: 0,
+  level1: {
+    data: 1,
+    level2: {
+      data: 2,
+      level3: {
+        data: 3
+      }
+    }
+  }
+};
+
+const obj2 = update(obj1, 'level1.level2.data'.split('.'), 99);
+
+console.log(JSON.stringify(obj1));
+console.log(JSON.stringify(obj2));