34 lines
867 B
Markdown
34 lines
867 B
Markdown
---
|
|
title: Find last matching key
|
|
tags: object
|
|
expertise: intermediate
|
|
cover: blog_images/sparkles.jpg
|
|
firstSeen: 2018-01-23T18:23:20+02:00
|
|
lastUpdated: 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'
|
|
```
|