const breadthFirstSearch = (graph, start, end) => {
  const queue = graph[start];
  const checked = [];

  let lastLevelElement = queue[queue.length - 1];
  let level = 1;


  while (queue.length) {
    const candidate = queue.shift();

    if (candidate === end) {
      return level;
    }

    if (checked.includes(candidate)) {
      continue;
    }

    queue.push(...(graph[candidate] || []));
    if (candidate === lastLevelElement) {
      lastLevelElement = queue[queue.length - 1];
      level += 1;
    }
  }

  return -1;
}

const graph = {
  a: ['b', 'c', 'd'],
  b: ['e', 'f'],
  d: ['e', 'g'],
  c: ['j', 'k'],
  e: ['l']
}

const res = breadthFirstSearch(graph, 'a', 'l');
console.log('res', res);