实施拓扑排序时遇到问题

Question

我已经尝试了几个小时，试图弄清楚如何实现Topsort的实际DFS部分，但是没有运气，而且我的Foreach部分一直出现错误。我的代码如下：

unction dfs(i, at, visited, ordering, graph) {
  
  visited[at] = true; //Set node as visited

  let edges = graph[at];

  edges.forEach(edge => {
    if (!visited[edge]) 
        i = dfs(i, edge.to, visited, ordering, graph);
  });

  ordering[i] = at; //Place node 
  return i - 1; //Decrement index

}

function topsort(graph) {
  let n = graph.length;
  let visited = []; //Tracks whether node has been visited
  for (a = 0; a < n; a++) { 
      visited[a] = null; //Initialize all nodes as null and unvisited
    };
 
  let ordering = []; //Array holds final topological order  
  let i = n - 1; //Insertion position of the next element in topo order. Insertions begin in the back which is why i = n-1

  for (at = 0; at < n; at++) { //Iterate over nodes
    if (!visited[at]) { //If a node has not been visited, initiate DFS
      i = dfs(i, at, visited, ordering, graph)
    };

  }

  return ordering;

}

let graph = [
    [1],
    [0, 4, 5],
    [3, 4, 5],
    [2, 6],
    [1, 2],
    [1, 2, 6],
    [3, 5],
    [],
    ];

let top = topsort(graph);

console.log(top);

运行以下链接中的代码：https://repl.it/@Stylebender/Topological-Sort#index.js

任何人都可以给我一些指示怎么做吗？