diff --git a/functional-tools.js b/functional-tools.js
index 8b13789..e79ab64 100644
--- a/functional-tools.js
+++ b/functional-tools.js
@@ -1 +1,29 @@
 
+/**
+ * Returns a JSON with an updated value
+ * @param {string} key
+ * @param {string} newValue
+ * @param {JSON} json
+ * @returns {JSON}
+ *
+ * Example
+ * const person = {name: 'James', age: 20, pets: ['dog', 'cat']};
+ * updateJSON('name', 'maria', person);
+ * // {"age": 20, "name": "maria", "pets": ["dog", "cat"]}
+ *
+ * Others: "modify" in Ramda
+ */
+function updateJSON(key, newValue, json) {
+    // JSON to Array
+    return Object.entries(json).map(
+        function (row) {
+            // Replace value
+            return row[0] == key ? row.slice(0, 1).concat(newValue) : row
+        }
+    ).reduce(
+        function (jsonUpdate, valueUpdate) {
+            // Array to JSON
+            jsonUpdate[valueUpdate[0]] = valueUpdate[1];
+            return jsonUpdate;
+        }, {});
+}