I think that sorting goes first by the left column, then by the right, sorting equal values of the first column.
const list = [{ first: 500, second: 1 }, { first: 500, second: 4 }, { first: 300, second: 2 }];
list.sort((a, b) => b.first - a.first); // A <- Z
list.sort((a, b) => a.first === b.first ? a.second - b.second : 1); // A -> Z