A depth first searching function :)

depthFirstSearch.js

function depthFirstSearch(tree, searchTerm) { // accepts standard object
  if (typeof searchTerm === 'number') {
    searchTerm = String(searchTerm);
  }
  if (typeof searchTerm !== 'string') {
    return null;
  }
  
  const objKeys = Object.keys(tree);

  for (let key of objKeys) {
    if (key === searchTerm) {
      return tree[key];
    }
    if (typeof tree[key] === 'object') {
      const returnValue = depthFirstSearch(tree[key], searchTerm);
      if (returnValue !== null) {
        return returnValue;
      }
    }
  }

  return null;
}

// ------- Alternative graph implementation --------

function depthFirstGraph(graph, searchTerm) {
    for (let key in graph) {
        function searchKey(graphKey) {
            if (graphKey === searchTerm) {
                return {
                    value: graph[graphKey]
                };
            } else {
                const arr = graph[graphKey];
                if (!arr.length) return null
                for (let index in arr) {
                    const result = searchKey(arr[index]);
                    if (result && result.value) return result;
                }
            }
        }

        const result = searchKey(key);
        if (result && !Array.isArray(result)) return result.value;
    }
    return null;
}

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