es-toolkit/docs/reference/array/intersectionWith.md

# intersectionWith

Returns the intersection of two arrays based on a custom equality function.

This function takes two arrays and a custom equality function. It returns a new array containing
the elements from the first array that have matching elements in the second array, as determined
by the custom equality function. It effectively filters out any elements from the first array that
do not have corresponding matches in the second array according to the equality function.

## Signature

```typescript
function intersectionWith<T>(firstArr: T[], secondArr: T[], areItemsEqual: (x: T, y: T) => boolean): T[];
```

### Parameters

- `firstArr` (`T[]`): The first array to compare.
- `secondArr` (`T[]`): The second array to compare.
- `areItemsEqual` (`(x: T, y: T) => boolean`): A custom function to determine if two elements are equal. This function takes two arguments, one from each array, and returns `true` if the elements are considered equal, and `false` otherwise.

### Returns

(`T[]`) A new array containing the elements from the first array that have corresponding matches in the second array according to the custom equality function.

## Examples

```typescript
const array1 = [{ id: 1 }, { id: 2 }, { id: 3 }];
const array2 = [{ id: 2 }, { id: 4 }];
const areItemsEqual = (a, b) => a.id === b.id;
const result = intersectionWith(array1, array2, areItemsEqual);
// result will be [{ id: 2 }] since this element has a matching id in both arrays.
```