25 lines
658 B
Markdown
25 lines
658 B
Markdown
---
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title: findKey
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tags: object,function,intermediate
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---
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Returns the first key that satisfies the provided testing function. Otherwise `undefined` is returned.
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- Use `Object.keys(obj)` to get all the properties of the object, `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 findKey = (obj, fn) => Object.keys(obj).find(key => fn(obj[key], key, obj));
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```
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```js
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findKey(
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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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o => o['active']
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); // 'barney'
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```
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