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The colleciton.last() method returns the last item in the collection. It does not remove the item from the collection:

Example

const collection = Collect([ 1, 2, 3 ])

await collection.last()

// 3

await collection.all()

// [ 1, 2, 3 ]

It wouuld be great to let users pass an (async) testing function as a parameter to the last method:

await Collect([
  { id: 1, name: 'marcus' },
  { id: 3, name: 'marcus' }
]).last(async ({ id }) => {
  return await User.findById(id)
})

// { id: 3, name: 'marcus', username: 'marcus' }

The collection.avg() method returns the average of all collection items:

Example

await Collect([1, 2, 3, 4])
  .avg()

// 2,5

Bonus
Create an alias method .average() that calls .avg() internally.

The collection.union(array) method adds all values from the array and removes duplicates:

Example

await Collect([1, 2, 3])
  .union([2, 3, 4, 5])
  .all()

// [1, 2, 3, 4, 5]

The collection.median() method returns the median value of the collection:

Example

await Collect([4, 1, 37, 2, 1])
  .median()

// 2

await Collect([1, 2, 3, 4, 5, 6])
  .median()

// 3.5

The collection.hasDuplicates() method determines whether the collection contains duplicate items.

Example

const collection = Collect([1, 2, 1, 3, 4])

await collection.hasDuplicates()

// true

const collection = Collect([1, 2, 3, 4])

await collection.hasDuplicates()

// false

The collection.toJSON() method creates a JSON string from the values of the collection:

Example

await Collect([1, 2, 3])
  .toJSON()

// "[1,2,3]"

await Collect([{ name: 'Marcus'}])
  .toJSON()

// "[{"name":"Marcus"}]"

I am not a user of any functional library but I have an idea what they do. Can you @marcuspoehls explain what the difference between this collections and any other library?

Reference: https://superchargejs.com/docs/master/collections#pluck

I'm going to add tiny feature to .pluck(): search by nested key. But I have one question about key parameter.

Which of the two options for specifying a key is better: key.nested_key_1.nested_key_2 or key[nested_key_1][nested_key_2] ?

It seems that 2nd variant looks better because it covers more variants of key (for ex.: string with spaces)

The collection.sum() method returns the sum of all collection items:

Example

await Collect([1, 2, 3, 4])
  .sum()

// 10

The collection.pop() method removes and returns the last item from the collection:

Example

const collection = Collect([4, 1, 37, 2, 12])

await collection.pop()

// 12

await collection.all()

// [4, 1, 37, 2]

The collection.max() method returns the max value in the collection:

Example

await Collect([1, 20, 3, 4])
  .max()

// 20

The collection.min() method returns the min value in the collection:

Example

await Collect([10, 2, 3, 4])
  .min()

// 2

The collection.reverse() method reverses the collection. The first item becomes the last one, the second item becomes the second to last, and so on:

Example

await Collect([4, 6, 8, 9])
  .reverse()
  .all()

// [9, 8, 6, 4]

The collection.sort() method returns the sorted collection:

Example

await Collect([4, 1, 37, 2, 1])
  .sort()
  .all()

// [1, 1, 2, 4, 37]

Hint: this is helpful when implementing #21

The collection.diff(array) method removes all values from the collection that are present in the given array.

Example

await Collect([1, 2, 3])
  .diff([2, 3, 4, 5])
  .all()

// [1]

The collection.join(str) method joins all items in the collection using the given str and returns the resulting string value:

Example

await Collect([10, 2, 3, 4])
  .join('-')

// '10-2-3-4' 

The collection.intersect(array) method removes all values from the collection that are not present in the given array.

Example

await Collect([1, 2, 3])
  .intersect([2, 3, 4, 5])
  .all()

// [2, 3]

Add a new .includes(value|predicate-fn) method that determines whether the collection includes a certain value. The .includes() method allows either a dedicated value or a predicate function receiving a collection item (like .find()).

Returns true if the value is found in the collection or the predicate function returns an item from the collection. Returns false otherwise.

Notice: this is basically an alias for the existing .has method.

Example

const collection = Collect([ 1, 2, 3 ])

await collection.includes(2)
// true

await collection.includes((value => {
  return value > 5
})
// false