8ee50178f3
Correct: `Array.from()` (it’s a static method) Incorrect: `Array.join()` (doesn’t exist; it’s a prototype method) This patch uses the common `#` syntax to denote `.prototype.`.
26 lines
697 B
Markdown
26 lines
697 B
Markdown
### findLastKey
|
|
|
|
Returns the last key that satisfies the provided testing function.
|
|
Otherwise `undefined` is returned.
|
|
|
|
Use `Object.keys(obj)` to get all the properties of the object, `Array.prototype.reverse()` to reverse their 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 }
|
|
},
|
|
o => o['active']
|
|
); // 'pebbles'
|
|
```
|