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.`.
21 lines
608 B
Markdown
21 lines
608 B
Markdown
### findKey
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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. 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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