A solution with reduce could look like:
const groceryList = ['apple', 'orange', 'celery', 'pineapple']
const { fiber, juices: modifiedList } = groceryList
.reduce((result, item) => {
if (item !== 'celery') {
result.juices.push(item)
} else {
result.fiber = item
}
return result
}, { fiber: undefined, juices: [] })
No side effects. Nice and clean.