27 lines
795 B
Markdown
27 lines
795 B
Markdown
---
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title: Check if array elements are equal based on function
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type: snippet
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language: javascript
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tags: [array]
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cover: orange-coffee-2
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dateModified: 2020-10-19T22:14:49+03:00
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---
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Checks if all elements in an array are equal, based on the provided mapping function.
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- Apply `fn` to the first element of `arr`.
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- Use `Array.prototype.every()` to check if `fn` returns the same value for all elements in the array as it did for the first one.
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- Elements in the array are compared using the strict comparison operator, which does not account for `NaN` self-inequality.
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```js
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const allEqualBy = (arr, fn) => {
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const eql = fn(arr[0]);
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return arr.every(val => fn(val) === eql);
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};
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```
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```js
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allEqualBy([1.1, 1.2, 1.3], Math.round); // true
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allEqualBy([1.1, 1.3, 1.6], Math.round); // false
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```
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