Start of main content## Recommended snippets

Returns the elements that exist in both arrays, using a provided comparator function.

- Use
`Array.prototype.filter()`

and`Array.prototype.findIndex()`

in combination with the provided comparator to determine intersecting values.

```
const intersectionWith = (a, b, comp) =>
a.filter(x => b.findIndex(y => comp(x, y)) !== -1);
```

```
intersectionWith(
[1, 1.2, 1.5, 3, 0],
[1.9, 3, 0, 3.9],
(a, b) => Math.round(a) === Math.round(b)
); // [1.5, 3, 0]
```

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### Array intersection based on function

JavaScript, Array

Returns the elements that exist in both arrays, after applying the provided function to each array element of both.

### Array union based on function

JavaScript, Array

Returns every element that exists in any of the two arrays at least once, using a provided comparator function.

### Mapped array union

JavaScript, Array

Returns every element that exists in any of the two arrays at least once, after applying the provided function to each array element of both.