groupby.js

// 成绩等级分为A、B和C三级
function getGrade(score) {
  return score < 60 ? 'C' :
    score < 80 ? 'B' : 'A';
};
// 学生及其成绩
let students = [
  { name: '张三', score: 84 },
  { name: '李四', score: 58 },
  { name: '王五', score: 99 },
  { name: '赵六', score: 69 }
];

function groupBy(students) {
  return [{}].concat(students).reduce((s, c) => {
    const grade = getGrade(c.score);
    !s[grade] && (s[grade] = []);
    s[grade].push(c);
    return s;
  })
}

// console.log(groupBy(students));

parse.js

function parse(input) {
  if (/^Array/.test(input)) {
    const type = /Array<(.+)>/.exec(input)[1];

    return {
      type: 'Array',
      typeArgs: parse(type)
    };
  }

  return { type: input };
}

const input = ["int", "string", "bool", "Array<int>", "Array<Array<int>>", "Array<Array<Array<int>>>"];

input.forEach(d => {
  console.log('----------------------');
  console.log(JSON.stringify(parse(d), null, '\t'));
});

tree.js

const assert = require('assert');

let tree = {
  id: '1',
  label: 'first',
  children: [
    {
      id: '2',
      label: 'second'
    },
    {
      id: '3',
      label: 'third',
      children: [
        {
          id: '4',
          label: 'fourth'
        },
        {
          id: '5',
          label: 'fifth'
        }
      ]
    }
  ]
};

function findNodeById(root = {}, id) {
  const p = root;

  if (!root.id) {
    return;
  }

  if (root.id === id) {
    return p;
  }

  if (!root.children) {
    return;
  }

  for (let i = 0; i < root.children.length; i++) {
    const ret = findNodeById(root.children[i], id);

    if (ret) {
      return ret
    }
  }
}

assert.equal(findNodeById(tree, '1').label, 'first');
assert.equal(findNodeById(tree, '2').label, 'second');
assert.equal(findNodeById(tree, '3').label, 'third');
assert.equal(findNodeById(tree, '4').label, 'fourth');
assert.equal(findNodeById(tree, '5').label, 'fifth');

cool ，尝试 parse 一下这个 case ：
Map<string, Array<Map<int, string>>>
Map<Array<Map<int, string>>, string>