30 lines
740 B
Markdown
30 lines
740 B
Markdown
---
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title: findLastKey
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tags: object,intermediate
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---
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Finds the last key that satisfies the provided testing function.
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Otherwise `undefined` is returned.
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- Use `Object.keys(obj)` to get all the properties of the object.
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- Use `Array.prototype.reverse()` to reverse the order and `Array.prototype.find()` to test the provided function for each key-value pair.
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- The callback receives three arguments - the value, the key and the object.
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```js
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const findLastKey = (obj, fn) =>
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Object.keys(obj)
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.reverse()
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.find(key => fn(obj[key], key, obj));
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```
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```js
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findLastKey(
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{
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barney: { age: 36, active: true },
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fred: { age: 40, active: false },
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pebbles: { age: 1, active: true }
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},
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x => x['active']
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); // 'pebbles'
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```
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