34 lines
837 B
Markdown
34 lines
837 B
Markdown
---
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title: Find last matching key
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type: snippet
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language: javascript
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tags: [object]
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cover: contemporary-desk
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dateModified: 2020-10-22T20:23:47+03:00
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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()` 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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