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javascript/snippets/find-last-key.md

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+---
+title: Find last matching key
+type: snippet
+tags: [object]
+cover: sparkles
+dateModified: 2020-10-22T20:23:47+03:00
+---
+
+Finds the last key that satisfies the provided testing function.
+Otherwise `undefined` is returned.
+
+- Use `Object.keys()` to get all the properties of the object.
+- Use `Array.prototype.reverse()` to reverse the order and `Array.prototype.find()` to test the provided function for each key-value pair.
+- The callback receives three arguments - the value, the key and the object.
+
+```js
+const findLastKey = (obj, fn) =>
+  Object.keys(obj)
+    .reverse()
+    .find(key => fn(obj[key], key, obj));
+```
+
+```js
+findLastKey(
+  {
+    barney: { age: 36, active: true },
+    fred: { age: 40, active: false },
+    pebbles: { age: 1, active: true }
+  },
+  x => x['active']
+); // 'pebbles'
+```