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snippets/js/s/find-key.md

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