find shortest route from coordinate in typescript

index.ts
interface Graph {
  [key: string]: { [key: string]: number };
}

function dijkstra(graph: Graph, start: string, end: string): number {
  const nodes = new Set(Object.keys(graph));
  const distances: { [key: string]: number } = {};
  const previous: { [key: string]: string } = {};

  for (const node of nodes) {
    distances[node] = Infinity;
  }
  distances[start] = 0;

  while (nodes.size > 0) {
    let smallest = null;
    for (const node of nodes) {
      if (smallest === null || distances[node] < distances[smallest]) {
        smallest = node;
      }
    }

    if (smallest === end) {
      let path = [];
      while (previous[smallest]) {
        path.push(smallest);
        smallest = previous[smallest];
      }
      return path.reverse();
    }

    nodes.delete(smallest);
    for (const neighbor in graph[smallest]) {
      const distance = graph[smallest][neighbor];
      const alt = distances[smallest] + distance;
      if (alt < distances[neighbor]) {
        distances[neighbor] = alt;
        previous[neighbor] = smallest;
      }
    }
  }
  return -1;
}
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