What is the unique() method in Collect.js?

Collect.js - Interview Questions

unique() : The unique() method returns all of the unique items in the collection:

const collection = collect([1, 1, 1, 2, 3, 3]);

const unique = collection.unique();

unique.all();

// [1, 2, 3]

When dealing with an array of objects, you may specify the key used to determine uniqueness:

const collection = collect([
  { name: 'iPhone 6', brand: 'Apple', type: 'phone' },
  { name: 'iPhone 5', brand: 'Apple', type: 'phone' },
  { name: 'Apple Watch', brand: 'Apple', type: 'watch' },
  { name: 'Galaxy S6', brand: 'Samsung', type: 'phone' },
  { name: 'Galaxy Gear', brand: 'Samsung', type: 'watch' },
]);

const unique = collection.unique('brand');

unique.all();

// [
//   { name: 'iPhone 6', brand: 'Apple', type: 'phone' },
//   { name: 'Galaxy S6', brand: 'Samsung', type: 'phone' },
// ]

You may also pass your own callback to determine item uniqueness :

const collection = collect([
  { name: 'iPhone 6', brand: 'Apple', type: 'phone' },
  { name: 'iPhone 5', brand: 'Apple', type: 'phone' },
  { name: 'Apple Watch', brand: 'Apple', type: 'watch' },
  { name: 'Galaxy S6', brand: 'Samsung', type: 'phone' },
  { name: 'Galaxy Gear', brand: 'Samsung', type: 'watch' },
]);

const unique = collection.unique(item => item.brand + item.type);

unique.all();

// [
//   { name: 'iPhone 6', brand: 'Apple', type: 'phone' },
//   { name: 'Apple Watch', brand: 'Apple', type: 'watch' },
//   { name: 'Galaxy S6', brand: 'Samsung', type: 'phone' },
//   { name: 'Galaxy Gear', brand: 'Samsung', type: 'watch' },
// ]