Explain unless() methods in Collect.js.

Collect.js - Interview Questions

unless() : The unless() method will execute the given callback when the first argument given to the method evaluates to false:

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

collection.unless(false, items => items.push(4));

collection.all();

// [1, 2, 3, 4]

unlessEmpty() : Alias for the whenNotEmpty() method

unlessNotEmpty() : Alias for the whenEmpty() method