In ES6, when the three dot notation (...) is used in a function declaration, it defines a rest parameter; when it is used with an array, it spreads the array's elements. You can pass each element of the array to a function in this way. You can also use it in array literals.

Let's see the following example:

1. let urgentTasks = ['Buy three tickets'];
2. let normalTasks = ['Book a hotel', 'Rent a car'];
3. let allTasks = [...urgentTasks, ...normalTasks];
4. 
5. ((first, second) => {
6.   console.log('Working on ' + first + ' and ' + second)
7. })(...allTasks);

In line 3, we use spread syntax to expand the urgentTasks array and the normalTasks array. And in line 7, we use spread syntax to expand the allTasks array and pass each element of it as arguments of the function. And the first argument has the value Buy three tickets, while the second argument has the value Book a hotel.