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.`.
18 lines
593 B
Markdown
18 lines
593 B
Markdown
### differenceBy
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Returns the difference between two arrays, after applying the provided function to each array element of both.
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Create a `Set` by applying `fn` to each element in `b`, then use `Array.prototype.filter()` in combination with `fn` on `a` to only keep values not contained in the previously created set.
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```js
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const differenceBy = (a, b, fn) => {
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const s = new Set(b.map(v => fn(v)));
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return a.filter(x => !s.has(fn(x)));
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};
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```
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```js
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differenceBy([2.1, 1.2], [2.3, 3.4], Math.floor); // [1.2]
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differenceBy([{ x: 2 }, { x: 1 }], [{ x: 1 }], v => v.x); // [ { x: 2 } ]
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```
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