...list
is using the spread syntax to spread the elements of list
. Let’s assume the list is [1, 2, 3]
. Therefore [...list, 0]
becomes:
[1, 2, 3, 0]
Which has the same result as doing list.concat([0]);
This is not a feature of the array in ES6, it’s just been used for array concatenation. It has other uses. Read more on MDN, or see this question.