javascript es6 array feature [...data, 0] "spread operator"
...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.
...list spreads (lays) out all the elements in the array list.
so [...list, 0] is all of the elements of list with a 0 at the end